Knightin todennäköisyys jäädä shakkilaudalle

Knightin todennäköisyys jäädä shakkilaudalle
Kokeile sitä GfG Practicessa

Koska a n*n shakkilauta ja ritari asema (x y) aina kun ritari liikkuu, se valitsee yhden kahdeksasta mahdollisesta liikkeestä tasaisesti satunnainen (vaikka nappula lähtisi shakkilaudalta) ja liikkeet siellä. Ritari jatkuu liikkuu, kunnes se on tehnyt tarkalleen k liikkuu tai on muutti pois shakkilaudalla. Tehtävänä on löytää the todennäköisyys että ritari jää päällä hallitus sen jälkeen kun on pysähtyi liikkuvat.

Huomautus: Shakkiritari voi tehdä kahdeksan mahdollista siirtoa. Jokainen liike on kaksi solua kardinaalisuunnassa ja yksi solu ortogonaalisessa suunnassa.

Esimerkkejä:  

Syöte: n = 8 x = 0 y = 0 k = 1
Lähtö: 0,25
Selitys: Ritari aloittaa kohdasta (0 0) ja yhden askeleen ottamisen jälkeen se makaa laudan sisällä vain kahdessa kahdeksasta asennosta, jotka ovat (1 2) ja (2 1). Tällöin todennäköisyys on 2/8 = 0,25.

Syöte: n = 8 x = 0 y = 0 k = 3
Lähtö: 0,125

Syöte: n = 4 x = 1 y = 2 k = 4
Lähtö: 0,024414

Sisällysluettelo

Ylhäältä alas Dp:n käyttö (muistiinmuokkaus) - O(n*n*k) aika ja O(n*n*k) tila

Todennäköisyys, että ritari jää shakkilaudalle k siirron jälkeen, on yhtä suuri kuin ritarin todennäköisyys edellisessä kahdeksassa paikassa k - 1 siirron jälkeen. Vastaavasti todennäköisyys k-1 liikkeen jälkeen riippuu todennäköisyyden keskiarvosta k-2 liikkeen jälkeen. Ideana on käyttää muistiinpano tallentaaksesi aikaisempien liikkeiden todennäköisyydet ja löytääksesi niiden keskiarvon lopputuloksen laskemiseksi.
Luo tätä varten a 3D-taulukkomuistio[][][] jossa muistio[i][j][k] tallentaa todennäköisyyden, että ritari on solussa (i j) k liikkeen jälkeen. Jos k on nolla, eli alkutila on saavutettu paluu 1 muuten tutkia edellistä kahdeksaa paikkaa ja löytää niiden todennäköisyyksien keskiarvo.

C++
   // C++ program to find the probability of the   // knight to remain inside the chessboard   #include          using     namespace     std  ;   // recursive function to calculate   // knight probability   double     knightProbability  (  int     n       int     x       int     y       int     k           vector   <  vector   <  vector   <  double  >>>     &  memo  ){      // Base case initial probability      if  (  k     ==     0  )     return     1.0  ;      // check if already calculated      if  (  memo  [  x  ][  y  ][  k  ]     !=     -1  )     return     memo  [  x  ][  y  ][  k  ];      vector   <  vector   <  int  >>     directions     =     {{  1       2  }     {  2       1  }     {  2       -1  }      {  1       -2  }     {  -1       -2  }     {  -2       -1  }     {  -2       1  }     {  -1       2  }};      memo  [  x  ][  y  ][  k  ]     =     0  ;      double     cur     =     0.0  ;      // for every position reachable from (xy)      for  (  auto     d  :  directions  ){      int     u     =     x     +     d  [  0  ];      int     v     =     y     +     d  [  1  ];      // if this position lie inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )      cur     +=     knightProbability  (  n       u       v       k  -1       memo  )     /     8.0  ;      }      return     memo  [  x  ][  y  ][  k  ]     =     cur  ;   }   // Function to find the probability   double     findProb  (  int     n       int     x       int     y       int     k  )     {      // Initialize memo to store results      vector   <  vector   <  vector   <  double  >>>     memo  (  n           vector   <  vector   <  double  >>  (  n        vector   <  double  >     (  k  +  1       -1  )));      return     knightProbability  (  n       x       y       k       memo  );   }   int     main  (){      int     n     =     8       x     =     0       y     =     0       k     =     3  ;      cout      < <     findProb  (  n       x       y       k  )      < <     endl  ;      return     0  ;   }   
Java
   // Java program to find the probability of the   // knight to remain inside the chessboard   class   GfG     {      // recursive function to calculate      // knight probability      static     double     knightProbability  (  int     n       int     x           int     y       int     k       double  [][][]     memo  )     {      // Base case initial probability      if     (  k     ==     0  )     return     1.0  ;      // check if already calculated      if     (  memo  [  x  ][  y  ][  k  ]     !=     -  1  )     return     memo  [  x  ][  y  ][  k  ]  ;      int  [][]     directions     =     {{  1       2  }     {  2       1  }     {  2       -  1  }     {  1       -  2  }      {  -  1       -  2  }     {  -  2       -  1  }     {  -  2       1  }     {  -  1       2  }};      memo  [  x  ][  y  ][  k  ]     =     0  ;      double     cur     =     0.0  ;      // for every position reachable from (x y)      for     (  int  []     d     :     directions  )     {      int     u     =     x     +     d  [  0  ]  ;      int     v     =     y     +     d  [  1  ]  ;      // if this position lies inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )      cur     +=     knightProbability  (  n       u       v       k     -     1       memo  )     /     8.0  ;      }      return     memo  [  x  ][  y  ][  k  ]     =     cur  ;      }      // Function to find the probability      static     double     findProb  (  int     n       int     x       int     y       int     k  )     {      // Initialize memo to store results      double  [][][]     memo     =     new     double  [  n  ][  n  ][  k     +     1  ]  ;      for     (  int     i     =     0  ;     i      <     n  ;     i  ++  )     {      for     (  int     j     =     0  ;     j      <     n  ;     j  ++  )     {      for     (  int     m     =     0  ;     m      <=     k  ;     m  ++  )     {      memo  [  i  ][  j  ][  m  ]     =     -  1  ;      }      }      }      return     knightProbability  (  n       x       y       k       memo  );      }      public     static     void     main  (  String  []     args  )     {      int     n     =     8       x     =     0       y     =     0       k     =     3  ;      System  .  out  .  println  (  findProb  (  n       x       y       k  ));      }   }   
Python
   # Python program to find the probability of the   # knight to remain inside the chessboard   # recursive function to calculate   # knight probability   def   knightProbability  (  n     x     y     k     memo  ):   # Base case initial probability   if   k   ==   0  :   return   1.0   # check if already calculated   if   memo  [  x  ][  y  ][  k  ]   !=   -  1  :   return   memo  [  x  ][  y  ][  k  ]   directions   =   [   [  1     2  ]   [  2     1  ]   [  2     -  1  ]   [  1     -  2  ]   [  -  1     -  2  ]   [  -  2     -  1  ]   [  -  2     1  ]   [  -  1     2  ]   ]   memo  [  x  ][  y  ][  k  ]   =   0   cur   =   0.0   # for every position reachable from (x y)   for   d   in   directions  :   u   =   x   +   d  [  0  ]   v   =   y   +   d  [  1  ]   # if this position lies inside the board   if   0    <=   u    <   n   and   0    <=   v    <   n  :   cur   +=   knightProbability  (  n     u     v     k   -   1     memo  )   /   8.0   memo  [  x  ][  y  ][  k  ]   =   cur   return   cur   # Function to find the probability   def   findProb  (  n     x     y     k  ):   # Initialize memo to store results   memo   =   [[[  -  1   for   _   in   range  (  k   +   1  )]   for   _   in   range  (  n  )]   for   _   in   range  (  n  )]   return   knightProbability  (  n     x     y     k     memo  )   n     x     y     k   =   8     0     0     3   print  (  findProb  (  n     x     y     k  ))   
C#
   // C# program to find the probability of the   // knight to remain inside the chessboard   using     System  ;   class     GfG     {      // recursive function to calculate      // knight probability      static     double     KnightProbability  (  int     n       int     x           int     y       int     k       double  []     memo  )     {      // Base case initial probability      if     (  k     ==     0  )     return     1.0  ;      // check if already calculated      if     (  memo  [  x       y       k  ]     !=     -  1  )     return     memo  [  x       y       k  ];      int  []     directions     =     {{  1       2  }     {  2       1  }     {  2       -  1  }     {  1       -  2  }      {  -  1       -  2  }     {  -  2       -  1  }     {  -  2       1  }     {  -  1       2  }};      memo  [  x       y       k  ]     =     0  ;      double     cur     =     0.0  ;      // for every position reachable from (x y)      for     (  int     i     =     0  ;     i      <     8  ;     i  ++  )     {      int     u     =     x     +     directions  [  i       0  ];      int     v     =     y     +     directions  [  i       1  ];      // if this position lies inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )     {      cur     +=     KnightProbability  (  n       u       v       k     -     1       memo  )     /     8.0  ;      }      }      return     memo  [  x       y       k  ]     =     cur  ;      }      // Function to find the probability      static     double     FindProb  (  int     n       int     x       int     y       int     k  )     {      // Initialize memo to store results      double  []     memo     =     new     double  [  n       n       k     +     1  ];      for     (  int     i     =     0  ;     i      <     n  ;     i  ++  )     {      for     (  int     j     =     0  ;     j      <     n  ;     j  ++  )     {      for     (  int     m     =     0  ;     m      <=     k  ;     m  ++  )     {      memo  [  i       j       m  ]     =     -  1  ;      }      }      }      return     KnightProbability  (  n       x       y       k       memo  );      }      static     void     Main  ()     {      int     n     =     8       x     =     0       y     =     0       k     =     3  ;      Console  .  WriteLine  (  FindProb  (  n       x       y       k  ));      }   }   
JavaScript
   // JavaScript program to find the probability of the   // knight to remain inside the chessboard   // recursive function to calculate   // knight probability   function     knightProbability  (  n       x       y       k       memo  )     {      // Base case initial probability      if     (  k     ===     0  )     return     1.0  ;      // check if already calculated      if     (  memo  [  x  ][  y  ][  k  ]     !==     -  1  )     return     memo  [  x  ][  y  ][  k  ];      const     directions     =     [      [  1       2  ]     [  2       1  ]     [  2       -  1  ]     [  1       -  2  ]      [  -  1       -  2  ]     [  -  2       -  1  ]     [  -  2       1  ]     [  -  1       2  ]      ];      memo  [  x  ][  y  ][  k  ]     =     0  ;      let     cur     =     0.0  ;      // for every position reachable from (x y)      for     (  let     d     of     directions  )     {      const     u     =     x     +     d  [  0  ];      const     v     =     y     +     d  [  1  ];      // if this position lies inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )     {      cur     +=     knightProbability  (  n       u       v       k     -     1       memo  )     /     8.0  ;      }      }      return     memo  [  x  ][  y  ][  k  ]     =     cur  ;   }   // Function to find the probability   function     findProb  (  n       x       y       k  )     {      // Initialize memo to store results      const     memo     =     Array  .  from  ({     length  :     n     }     ()     =>      Array  .  from  ({     length  :     n     }     ()     =>     Array  (  k     +     1  ).  fill  (  -  1  )));      return     knightProbability  (  n       x       y       k       memo  ).  toFixed  (  6  );   }   const     n     =     8       x     =     0       y     =     0       k     =     3  ;      console  .  log  (  findProb  (  n       x       y       k  ));   

Lähtö
0.125  

Alhaalta ylöspäin suuntautuva Dp (taulukko) - O(n*n*k) aika ja O(n*n*k) avaruus

Yllä oleva lähestymistapa voidaan optimoida käyttämällä alhaalta ylöspäin taulukointi vähentää rekursiivisen pinon vaatimaa ylimääräistä tilaa. Ajatuksena on säilyttää 3 D-taulukko dp[][][] jossa dp[i][j][k] tallentaa todennäköisyyden, että ritari on solussa (i j) jälkeen k liikkeet. Alusta 0 tilasta dp arvolla 1 . Jokaista seuraavaa siirtoa varten todennäköisyys ritari tulee olemaan yhtäläinen to keskimäärin todennäköisyydestä edellinen 8 paikkaa jälkeen k-1 liikkeet.

C++
   // C++ program to find the probability of the   // knight to remain inside the chessboard   #include          using     namespace     std  ;   // Function to find the probability   double     findProb  (  int     n       int     x       int     y       int     k  )     {      // Initialize dp to store results of each step      vector   <  vector   <  vector   <  double  >>>     dp  (  n           vector   <  vector   <  double  >>  (  n        vector   <  double  >     (  k  +  1  )));          // Initialize dp for step 0      for     (  int     i     =     0  ;     i      <     n  ;     ++  i  )     {      for     (  int     j     =     0  ;     j      <     n  ;     ++  j  )     {      dp  [  i  ][  j  ][  0  ]     =     1.0  ;      }      }      vector   <  vector   <  int  >>     directions     =     {      {  1       2  }     {  2       1  }     {  2       -1  }     {  1       -2  }         {  -1       -2  }     {  -2       -1  }     {  -2       1  }     {  -1       2  }      };      for     (  int     move     =     1  ;     move      <=     k  ;     move  ++  )     {          // find probability for cell (i j)      for     (  int     i     =     0  ;     i      <     n  ;     ++  i  )     {      for     (  int     j     =     0  ;     j      <     n  ;     ++  j  )     {      double     cur     =     0.0  ;      // for every position reachable from (xy)      for     (  auto     d  :  directions  )     {      int     u     =     i     +     d  [  0  ];      int     v     =     j     +     d  [  1  ];      // if this position lie inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )      cur     +=     dp  [  u  ][  v  ][  move     -     1  ]     /     8.0  ;      }      // store the result      dp  [  i  ][  j  ][  move  ]     =     cur  ;      }      }      }      // return the result      return     dp  [  x  ][  y  ][  k  ];   }   int     main  (){      int     n     =     8       x     =     0       y     =     0       k     =     3  ;      cout      < <     findProb  (  n       x       y       k  )      < <     endl  ;      return     0  ;   }   
Java
   // Java program to find the probability of the   // knight to remain inside the chessboard   import     java.util.*  ;   class   GfG     {      // Function to find the probability      static     double     findProb  (  int     n       int     x       int     y       int     k  )     {      // Initialize dp to store results of each step      double  [][][]     dp     =     new     double  [  n  ][  n  ][  k     +     1  ]  ;      for     (  int     i     =     0  ;     i      <     n  ;     i  ++  )     {      for     (  int     j     =     0  ;     j      <     n  ;     j  ++  )     {      dp  [  i  ][  j  ][  0  ]     =     1  ;      }      }      int  [][]     directions     =     {      {  1       2  }     {  2       1  }     {  2       -  1  }     {  1       -  2  }         {  -  1       -  2  }     {  -  2       -  1  }     {  -  2       1  }     {  -  1       2  }      };      for     (  int     move     =     1  ;     move      <=     k  ;     move  ++  )     {      // find probability for cell (i j)      for     (  int     i     =     0  ;     i      <     n  ;     ++  i  )     {      for     (  int     j     =     0  ;     j      <     n  ;     ++  j  )     {      double     cur     =     0.0  ;      // for every position reachable from (x y)      for     (  int  []     d     :     directions  )     {      int     u     =     i     +     d  [  0  ]  ;      int     v     =     j     +     d  [  1  ]  ;      // if this position lies inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )     {      cur     +=     dp  [  u  ][  v  ][  move     -     1  ]     /     8.0  ;      }      }      // store the result      dp  [  i  ][  j  ][  move  ]     =     cur  ;      }      }      }      // return the result      return     dp  [  x  ][  y  ][  k  ]  ;      }      public     static     void     main  (  String  []     args  )     {      int     n     =     8       x     =     0       y     =     0       k     =     3  ;      System  .  out  .  println  (  findProb  (  n       x       y       k  ));      }   }   
Python
   # Python program to find the probability of the   # knight to remain inside the chessboard   # Function to find the probability   def   findProb  (  n     x     y     k  ):   # Initialize dp to store results of each step   dp   =   [[[  0   for   _   in   range  (  k   +   1  )]   for   _   in   range  (  n  )]   for   _   in   range  (  n  )]   for   i   in   range  (  n  ):   for   j   in   range  (  n  ):   dp  [  i  ][  j  ][  0  ]   =   1.0   directions   =   [[  1     2  ]   [  2     1  ]   [  2     -  1  ]   [  1     -  2  ]   [  -  1     -  2  ]   [  -  2     -  1  ]   [  -  2     1  ]   [  -  1     2  ]]   for   move   in   range  (  1     k   +   1  ):   # find probability for cell (i j)   for   i   in   range  (  n  ):   for   j   in   range  (  n  ):   cur   =   0.0   # for every position reachable from (x y)   for   d   in   directions  :   u   =   i   +   d  [  0  ]   v   =   j   +   d  [  1  ]   # if this position lies inside the board   if   0    <=   u    <   n   and   0    <=   v    <   n  :   cur   +=   dp  [  u  ][  v  ][  move   -   1  ]   /   8.0   # store the result   dp  [  i  ][  j  ][  move  ]   =   cur   # return the result   return   dp  [  x  ][  y  ][  k  ]   if   __name__   ==   '__main__'  :   n     x     y     k   =   8     0     0     3   print  (  findProb  (  n     x     y     k  ))   
C#
   // C# program to find the probability of the   // knight to remain inside the chessboard   using     System  ;   class     GfG     {      // Function to find the probability      static     double     findProb  (  int     n       int     x       int     y       int     k  )     {      // Initialize dp to store results of each step      double  []     dp     =     new     double  [  n       n       k     +     1  ];      for     (  int     i     =     0  ;     i      <     n  ;     i  ++  )     {      for     (  int     j     =     0  ;     j      <     n  ;     j  ++  )     {      dp  [  i       j       0  ]     =     1.0  ;      }      }      int  []     directions     =     {{  1       2  }     {  2       1  }     {  2       -  1  }     {  1       -  2  }         {  -  1       -  2  }     {  -  2       -  1  }     {  -  2       1  }     {  -  1       2  }};      for     (  int     move     =     1  ;     move      <=     k  ;     move  ++  )     {      // find probability for cell (i j)      for     (  int     i     =     0  ;     i      <     n  ;     ++  i  )     {      for     (  int     j     =     0  ;     j      <     n  ;     ++  j  )     {      double     cur     =     0.0  ;      // for every position reachable from (x y)      for     (  int     d     =     0  ;     d      <     directions  .  GetLength  (  0  );     d  ++  )     {      int     u     =     i     +     directions  [  d       0  ];      int     v     =     j     +     directions  [  d       1  ];      // if this position lies inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )     {      cur     +=     dp  [  u       v       move     -     1  ]     /     8.0  ;      }      }      // store the result      dp  [  i       j       move  ]     =     cur  ;      }      }      }      // return the result      return     dp  [  x       y       k  ];      }      static     void     Main  (  string  []     args  )     {      int     n     =     8       x     =     0       y     =     0       k     =     3  ;      Console  .  WriteLine  (  findProb  (  n       x       y       k  ));      }   }   
JavaScript
   // JavaScript program to find the probability of the   // knight to remain inside the chessboard   // Function to find the probability   function     findProb  (  n       x       y       k  )     {      // Initialize dp to store results of each step      let     dp     =     Array  .  from  ({     length  :     n     }     ()     =>         Array  .  from  ({     length  :     n     }     ()     =>     Array  (  k     +     1  ).  fill  (  0  ))      );      // Initialize dp for step 0      for     (  let     i     =     0  ;     i      <     n  ;     ++  i  )     {      for     (  let     j     =     0  ;     j      <     n  ;     ++  j  )     {      dp  [  i  ][  j  ][  0  ]     =     1.0  ;      }      }          let     directions     =     [[  1       2  ]     [  2       1  ]     [  2       -  1  ]     [  1       -  2  ]         [  -  1       -  2  ]     [  -  2       -  1  ]     [  -  2       1  ]     [  -  1       2  ]];      for     (  let     move     =     1  ;     move      <=     k  ;     move  ++  )     {          // find probability for cell (i j)      for     (  let     i     =     0  ;     i      <     n  ;     i  ++  )     {      for     (  let     j     =     0  ;     j      <     n  ;     j  ++  )     {      let     cur     =     0.0  ;      // for every position reachable from (x y)      for     (  let     d     of     directions  )     {      let     u     =     i     +     d  [  0  ];      let     v     =     j     +     d  [  1  ];      // if this position lies inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )     {      cur     +=     dp  [  u  ][  v  ][  move     -     1  ]     /     8.0  ;      }      }      // store the result      dp  [  i  ][  j  ][  move  ]     =     cur  ;      }      }      }      // return the result      return     dp  [  x  ][  y  ][  k  ].  toFixed  (  6  );   }   let     n     =     8       x     =     0       y     =     0       k     =     3  ;   console  .  log  (  findProb  (  n       x       y       k  ));   

Lähtö
0.125  

Avaruuden käyttäminen Optimoitu Dp - O(n*n*k) aika ja O(n*n) avaruus

Yllä oleva lähestymistapa vaatii vain edellinen todennäköisyyksien tila laskea nykyinen ilmaista näin vain the edellinen myymälä on varastoitava. Ajatuksena on luoda kaksi 2d-taulukot prevMove[][] ja currMove[][] jossa

  • prevMove[i][j] tallentaa todennäköisyyden, että ritari on kohdassa (i j) edelliseen siirtoon asti. Se alustetaan alkutilan arvolla 1.
  • currMove[i][j] tallentaa nykyisen tilan todennäköisyyden.

Toimi samalla tavalla kuin yllä oleva lähestymistapa ja klo loppu jokaisesta iteraatiosta päivitä prevMove[][] johon on tallennettu arvo currMove[][].

C++
   // C++ program to find the probability of the   // knight to remain inside the chessboard   #include          using     namespace     std  ;   // Function to find the probability   double     findProb  (  int     n       int     x       int     y       int     k  )     {      // dp to store results of previous move      vector   <  vector   <  double  >>     prevMove  (  n       vector   <  double  >  (  n       1  ));      // dp to store results of current move      vector   <  vector   <  double  >>     currMove  (  n       vector   <  double  >  (  n       0  ));      vector   <  vector   <  int  >>     directions     =     {      {  1       2  }     {  2       1  }     {  2       -1  }     {  1       -2  }         {  -1       -2  }     {  -2       -1  }     {  -2       1  }     {  -1       2  }      };      for     (  int     move     =     1  ;     move      <=     k  ;     move  ++  )     {          // find probability for cell (i j)      for     (  int     i     =     0  ;     i      <     n  ;     ++  i  )     {      for     (  int     j     =     0  ;     j      <     n  ;     ++  j  )     {      double     cur     =     0.0  ;      // for every position reachable from (xy)      for     (  auto     d  :  directions  )     {      int     u     =     i     +     d  [  0  ];      int     v     =     j     +     d  [  1  ];      // if this position lie inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )      cur     +=     prevMove  [  u  ][  v  ]     /     8.0  ;      }      // store the result      currMove  [  i  ][  j  ]     =     cur  ;      }      }      // update previous state      prevMove     =     currMove  ;      }      // return the result      return     prevMove  [  x  ][  y  ];   }   int     main  (){      int     n     =     8       x     =     0       y     =     0       k     =     3  ;      cout      < <     findProb  (  n       x       y       k  )      < <     endl  ;      return     0  ;   }   
Java
   // Java program to find the probability of the   // knight to remain inside the chessboard   class   GfG     {      // Function to find the probability      static     double     findProb  (  int     n       int     x       int     y       int     k  )     {      // dp to store results of previous move      double  [][]     prevMove     =     new     double  [  n  ][  n  ]  ;      for     (  int     i     =     0  ;     i      <     n  ;     i  ++  )     {      for     (  int     j     =     0  ;     j      <     n  ;     j  ++  )     {      prevMove  [  i  ][  j  ]     =     1.0  ;      }      }      // dp to store results of current move      double  [][]     currMove     =     new     double  [  n  ][  n  ]  ;      int  [][]     directions     =     {      {  1       2  }     {  2       1  }     {  2       -  1  }     {  1       -  2  }      {  -  1       -  2  }     {  -  2       -  1  }     {  -  2       1  }     {  -  1       2  }      };      for     (  int     move     =     1  ;     move      <=     k  ;     move  ++  )     {      // find probability for cell (i j)      for     (  int     i     =     0  ;     i      <     n  ;     ++  i  )     {      for     (  int     j     =     0  ;     j      <     n  ;     ++  j  )     {      double     cur     =     0.0  ;      // for every position reachable from (xy)      for     (  int  []     d     :     directions  )     {      int     u     =     i     +     d  [  0  ]  ;      int     v     =     j     +     d  [  1  ]  ;      // if this position lies inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )      cur     +=     prevMove  [  u  ][  v  ]     /     8.0  ;      }      // store the result      currMove  [  i  ][  j  ]     =     cur  ;      }      }      // update previous state      for     (  int     i     =     0  ;     i      <     n  ;     i  ++  )     {      System  .  arraycopy  (  currMove  [  i  ]       0       prevMove  [  i  ]       0       n  );      }      }      // return the result      return     prevMove  [  x  ][  y  ]  ;      }      public     static     void     main  (  String  []     args  )     {      int     n     =     8       x     =     0       y     =     0       k     =     3  ;      System  .  out  .  println  (  findProb  (  n       x       y       k  ));      }   }   
Python
   # Python program to find the probability of the   # knight to remain inside the chessboard   def   findProb  (  n     x     y     k  ):   # dp to store results of previous move   prevMove   =   [[  1.0  ]   *   n   for   _   in   range  (  n  )]   # dp to store results of current move   currMove   =   [[  0.0  ]   *   n   for   _   in   range  (  n  )]   directions   =   [   [  1     2  ]   [  2     1  ]   [  2     -  1  ]   [  1     -  2  ]   [  -  1     -  2  ]   [  -  2     -  1  ]   [  -  2     1  ]   [  -  1     2  ]   ]   for   move   in   range  (  1     k   +   1  ):   # find probability for cell (i j)   for   i   in   range  (  n  ):   for   j   in   range  (  n  ):   cur   =   0.0   # for every position reachable from (xy)   for   d   in   directions  :   u     v   =   i   +   d  [  0  ]   j   +   d  [  1  ]   # if this position lies inside the board   if   0    <=   u    <   n   and   0    <=   v    <   n  :   cur   +=   prevMove  [  u  ][  v  ]   /   8.0   # store the result   currMove  [  i  ][  j  ]   =   cur   # update previous state   prevMove   =   [  row  [:]   for   row   in   currMove  ]   # return the result   return   prevMove  [  x  ][  y  ]   if   __name__   ==   '__main__'  :   n     x     y     k   =   8     0     0     3   print  (  findProb  (  n     x     y     k  ))   
C#
   // C# program to find the probability of the   // knight to remain inside the chessboard   using     System  ;   class     GfG     {      // Function to find the probability      static     double     findProb  (  int     n       int     x       int     y       int     k  )     {      // dp to store results of previous move      double  []     prevMove     =     new     double  [  n       n  ];      for     (  int     i     =     0  ;     i      <     n  ;     i  ++  )      for     (  int     j     =     0  ;     j      <     n  ;     j  ++  )      prevMove  [  i       j  ]     =     1.0  ;      // dp to store results of current move      double  []     currMove     =     new     double  [  n       n  ];      int  []     directions     =     {      {  1       2  }     {  2       1  }     {  2       -  1  }     {  1       -  2  }      {  -  1       -  2  }     {  -  2       -  1  }     {  -  2       1  }     {  -  1       2  }      };      for     (  int     move     =     1  ;     move      <=     k  ;     move  ++  )     {      // find probability for cell (i j)      for     (  int     i     =     0  ;     i      <     n  ;     ++  i  )     {      for     (  int     j     =     0  ;     j      <     n  ;     ++  j  )     {      double     cur     =     0.0  ;      // for every position reachable from (xy)      for     (  int     d     =     0  ;     d      <     directions  .  GetLength  (  0  );     d  ++  )     {      int     u     =     i     +     directions  [  d       0  ];      int     v     =     j     +     directions  [  d       1  ];      // if this position lies inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )      cur     +=     prevMove  [  u       v  ]     /     8.0  ;      }      // store the result      currMove  [  i       j  ]     =     cur  ;      }      }      // update previous state      Array  .  Copy  (  currMove       prevMove       n     *     n  );      }      // return the result      return     prevMove  [  x       y  ];      }      static     void     Main  ()     {      int     n     =     8       x     =     0       y     =     0       k     =     3  ;      Console  .  WriteLine  (  findProb  (  n       x       y       k  ));      }   }   
JavaScript
   // JavaScript program to find the probability of the   // knight to remain inside the chessboard   function     findProb  (  n       x       y       k  )     {      // dp to store results of previous move      let     prevMove     =     Array  .  from  ({     length  :     n     }         ()     =>     Array  (  n  ).  fill  (  1.0  ));      // dp to store results of current move      let     currMove     =     Array  .  from  ({     length  :     n     }         ()     =>     Array  (  n  ).  fill  (  0.0  ));      const     directions     =     [      [  1       2  ]     [  2       1  ]     [  2       -  1  ]     [  1       -  2  ]      [  -  1       -  2  ]     [  -  2       -  1  ]     [  -  2       1  ]     [  -  1       2  ]      ];      for     (  let     move     =     1  ;     move      <=     k  ;     move  ++  )     {      // find probability for cell (i j)      for     (  let     i     =     0  ;     i      <     n  ;     i  ++  )     {      for     (  let     j     =     0  ;     j      <     n  ;     j  ++  )     {      let     cur     =     0.0  ;      // for every position reachable from (xy)      for     (  let     d     of     directions  )     {      let     u     =     i     +     d  [  0  ];      let     v     =     j     +     d  [  1  ];      // if this position lies inside the board      if     (  u     >=     0     &&     u      <     n     &&     v     >=     0     &&     v      <     n  )      cur     +=     prevMove  [  u  ][  v  ]     /     8.0  ;      }      // store the result      currMove  [  i  ][  j  ]     =     cur  ;      }      }      // update previous state      prevMove     =     currMove  .  map  (  row     =>     [...  row  ]);      }      // return the result      return     prevMove  [  x  ][  y  ].  toFixed  (  6  );   }   let     n     =     8       x     =     0       y     =     0       k     =     3  ;   console  .  log  (  findProb  (  n       x       y       k  ));   

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