الحد الأدنى من الخطوات للوصول إلى الهدف بواسطة الفارس | مجموعة 2
بالنظر إلى رقعة شطرنج مربعة بحجم N x N، يتم إعطاء موضع الفارس وموضع الهدف، وتتمثل المهمة في معرفة الحد الأدنى من الخطوات التي سيتخذها الفارس للوصول إلى موضع الهدف.
أمثلة :
Input : (2 4) - knight's position (6 4) - target cell Output : 2 Input : (4 5) (1 1) Output : 3
لقد تمت بالفعل مناقشة نهج BFS لحل المشكلة المذكورة أعلاه في سابق بريد. في هذا المنشور تتم مناقشة حل البرمجة الديناميكية.
شرح المنهج :
دع رقعة الشطرنج مكونة من 8 × 8 خلية. الآن لنفترض أن الفارس عند (3 3) والهدف عند (7 8). هناك 8 حركات محتملة من الوضع الحالي للفارس، أي (2 1) (1 2) (4 1) (1 4) (5 2) (2 5) (5 4) (4 5). لكن من بين هذه الحركات فقط (5 4) و (4 5) ستكون نحو الهدف وكل ما عداها يذهب بعيداً عن الهدف. لذلك للعثور على الحد الأدنى من الخطوات، انتقل إلى (4 5) أو (5 4). الآن احسب الحد الأدنى من الخطوات المتخذة من (4 5) و (5 4) للوصول إلى الهدف. يتم حساب ذلك عن طريق البرمجة الديناميكية. وبالتالي ينتج عن ذلك الحد الأدنى من الخطوات من (3 3) إلى (7 8).
دع رقعة الشطرنج مكونة من 8 × 8 خلية. لنفترض الآن أن الفارس عند (4 3) والهدف عند (4 7). هناك 8 حركات محتملة ولكن نحو الهدف لا يوجد سوى 4 حركات أي (5 5) (3 5) (2 4) (6 4). حيث أن (5 5) يعادل (5 3) و(4 2) يعادل (4 6). إذن من هذه النقاط الأربع يمكن تحويلها إلى نقطتين. أخذ (5 5) و (6 4) (هنا). الآن احسب الحد الأدنى من الخطوات المتخذة من هاتين النقطتين للوصول إلى الهدف. يتم حساب ذلك عن طريق البرمجة الديناميكية. وبالتالي ينتج عن ذلك الحد الأدنى من الخطوات من (4 3) إلى (4 7).
استثناء : عندما يكون الفارس في الزاوية ويكون الهدف بحيث يكون الفرق بين إحداثيات x و y مع موضع الفارس هو (1 1) أو العكس. ثم الحد الأدنى من الخطوات سيكون 4.
معادلة البرمجة الديناميكية :
1) موانئ دبي[diffOfX][diffOfY] هو الحد الأدنى من الخطوات المتخذة من موقع الفارس إلى موقع الهدف.
2) dp[diffOfX][diffOfY] = dp[diffOfY][diffOfX] .
حيث diffOfX = الفرق بين إحداثي x للفارس وإحداثي x للهدف
diffOfY = الفرق بين إحداثي y للفارس وإحداثي y للهدف
فيما يلي تنفيذ النهج أعلاه:
// C++ code for minimum steps for // a knight to reach target position #include using namespace std ; // initializing the matrix. int dp [ 8 ][ 8 ] = { 0 }; int getsteps ( int x int y int tx int ty ) { // if knight is on the target // position return 0. if ( x == tx && y == ty ) return dp [ 0 ][ 0 ]; else { // if already calculated then return // that value. Taking absolute difference. if ( dp [ abs ( x - tx )][ abs ( y - ty )] != 0 ) return dp [ abs ( x - tx )][ abs ( y - ty )]; else { // there will be two distinct positions // from the knight towards a target. // if the target is in same row or column // as of knight then there can be four // positions towards the target but in that // two would be the same and the other two // would be the same. int x1 y1 x2 y2 ; // (x1 y1) and (x2 y2) are two positions. // these can be different according to situation. // From position of knight the chess board can be // divided into four blocks i.e.. N-E E-S S-W W-N . if ( x <= tx ) { if ( y <= ty ) { x1 = x + 2 ; y1 = y + 1 ; x2 = x + 1 ; y2 = y + 2 ; } else { x1 = x + 2 ; y1 = y - 1 ; x2 = x + 1 ; y2 = y - 2 ; } } else { if ( y <= ty ) { x1 = x - 2 ; y1 = y + 1 ; x2 = x - 1 ; y2 = y + 2 ; } else { x1 = x - 2 ; y1 = y - 1 ; x2 = x - 1 ; y2 = y - 2 ; } } // ans will be 1 + minimum of steps // required from (x1 y1) and (x2 y2). dp [ abs ( x - tx )][ abs ( y - ty )] = min ( getsteps ( x1 y1 tx ty ) getsteps ( x2 y2 tx ty )) + 1 ; // exchanging the coordinates x with y of both // knight and target will result in same ans. dp [ abs ( y - ty )][ abs ( x - tx )] = dp [ abs ( x - tx )][ abs ( y - ty )]; return dp [ abs ( x - tx )][ abs ( y - ty )]; } } } // Driver Code int main () { int i n x y tx ty ans ; // size of chess board n*n n = 100 ; // (x y) coordinate of the knight. // (tx ty) coordinate of the target position. x = 4 ; y = 5 ; tx = 1 ; ty = 1 ; // (Exception) these are the four corner points // for which the minimum steps is 4. if (( x == 1 && y == 1 && tx == 2 && ty == 2 ) || ( x == 2 && y == 2 && tx == 1 && ty == 1 )) ans = 4 ; else if (( x == 1 && y == n && tx == 2 && ty == n - 1 ) || ( x == 2 && y == n - 1 && tx == 1 && ty == n )) ans = 4 ; else if (( x == n && y == 1 && tx == n - 1 && ty == 2 ) || ( x == n - 1 && y == 2 && tx == n && ty == 1 )) ans = 4 ; else if (( x == n && y == n && tx == n - 1 && ty == n - 1 ) || ( x == n - 1 && y == n - 1 && tx == n && ty == n )) ans = 4 ; else { // dp[a][b] here a b is the difference of // x & tx and y & ty respectively. dp [ 1 ][ 0 ] = 3 ; dp [ 0 ][ 1 ] = 3 ; dp [ 1 ][ 1 ] = 2 ; dp [ 2 ][ 0 ] = 2 ; dp [ 0 ][ 2 ] = 2 ; dp [ 2 ][ 1 ] = 1 ; dp [ 1 ][ 2 ] = 1 ; ans = getsteps ( x y tx ty ); } cout < < ans < < endl ; return 0 ; }
Java //Java code for minimum steps for // a knight to reach target position public class GFG { // initializing the matrix. static int dp [][] = new int [ 8 ][ 8 ] ; static int getsteps ( int x int y int tx int ty ) { // if knight is on the target // position return 0. if ( x == tx && y == ty ) { return dp [ 0 ][ 0 ] ; } else // if already calculated then return // that value. Taking absolute difference. if ( dp [ Math . abs ( x - tx ) ][ Math . abs ( y - ty ) ] != 0 ) { return dp [ Math . abs ( x - tx ) ][ Math . abs ( y - ty ) ] ; } else { // there will be two distinct positions // from the knight towards a target. // if the target is in same row or column // as of knight then there can be four // positions towards the target but in that // two would be the same and the other two // would be the same. int x1 y1 x2 y2 ; // (x1 y1) and (x2 y2) are two positions. // these can be different according to situation. // From position of knight the chess board can be // divided into four blocks i.e.. N-E E-S S-W W-N . if ( x <= tx ) { if ( y <= ty ) { x1 = x + 2 ; y1 = y + 1 ; x2 = x + 1 ; y2 = y + 2 ; } else { x1 = x + 2 ; y1 = y - 1 ; x2 = x + 1 ; y2 = y - 2 ; } } else if ( y <= ty ) { x1 = x - 2 ; y1 = y + 1 ; x2 = x - 1 ; y2 = y + 2 ; } else { x1 = x - 2 ; y1 = y - 1 ; x2 = x - 1 ; y2 = y - 2 ; } // ans will be 1 + minimum of steps // required from (x1 y1) and (x2 y2). dp [ Math . abs ( x - tx ) ][ Math . abs ( y - ty ) ] = Math . min ( getsteps ( x1 y1 tx ty ) getsteps ( x2 y2 tx ty )) + 1 ; // exchanging the coordinates x with y of both // knight and target will result in same ans. dp [ Math . abs ( y - ty ) ][ Math . abs ( x - tx ) ] = dp [ Math . abs ( x - tx ) ][ Math . abs ( y - ty ) ] ; return dp [ Math . abs ( x - tx ) ][ Math . abs ( y - ty ) ] ; } } // Driver Code static public void main ( String [] args ) { int i n x y tx ty ans ; // size of chess board n*n n = 100 ; // (x y) coordinate of the knight. // (tx ty) coordinate of the target position. x = 4 ; y = 5 ; tx = 1 ; ty = 1 ; // (Exception) these are the four corner points // for which the minimum steps is 4. if (( x == 1 && y == 1 && tx == 2 && ty == 2 ) || ( x == 2 && y == 2 && tx == 1 && ty == 1 )) { ans = 4 ; } else if (( x == 1 && y == n && tx == 2 && ty == n - 1 ) || ( x == 2 && y == n - 1 && tx == 1 && ty == n )) { ans = 4 ; } else if (( x == n && y == 1 && tx == n - 1 && ty == 2 ) || ( x == n - 1 && y == 2 && tx == n && ty == 1 )) { ans = 4 ; } else if (( x == n && y == n && tx == n - 1 && ty == n - 1 ) || ( x == n - 1 && y == n - 1 && tx == n && ty == n )) { ans = 4 ; } else { // dp[a][b] here a b is the difference of // x & tx and y & ty respectively. dp [ 1 ][ 0 ] = 3 ; dp [ 0 ][ 1 ] = 3 ; dp [ 1 ][ 1 ] = 2 ; dp [ 2 ][ 0 ] = 2 ; dp [ 0 ][ 2 ] = 2 ; dp [ 2 ][ 1 ] = 1 ; dp [ 1 ][ 2 ] = 1 ; ans = getsteps ( x y tx ty ); } System . out . println ( ans ); } } /*This code is contributed by PrinciRaj1992*/
Python3 # Python3 code for minimum steps for # a knight to reach target position # initializing the matrix. dp = [[ 0 for i in range ( 8 )] for j in range ( 8 )]; def getsteps ( x y tx ty ): # if knight is on the target # position return 0. if ( x == tx and y == ty ): return dp [ 0 ][ 0 ]; # if already calculated then return # that value. Taking absolute difference. elif ( dp [ abs ( x - tx )][ abs ( y - ty )] != 0 ): return dp [ abs ( x - tx )][ abs ( y - ty )]; else : # there will be two distinct positions # from the knight towards a target. # if the target is in same row or column # as of knight then there can be four # positions towards the target but in that # two would be the same and the other two # would be the same. x1 y1 x2 y2 = 0 0 0 0 ; # (x1 y1) and (x2 y2) are two positions. # these can be different according to situation. # From position of knight the chess board can be # divided into four blocks i.e.. N-E E-S S-W W-N . if ( x <= tx ): if ( y <= ty ): x1 = x + 2 ; y1 = y + 1 ; x2 = x + 1 ; y2 = y + 2 ; else : x1 = x + 2 ; y1 = y - 1 ; x2 = x + 1 ; y2 = y - 2 ; elif ( y <= ty ): x1 = x - 2 ; y1 = y + 1 ; x2 = x - 1 ; y2 = y + 2 ; else : x1 = x - 2 ; y1 = y - 1 ; x2 = x - 1 ; y2 = y - 2 ; # ans will be 1 + minimum of steps # required from (x1 y1) and (x2 y2). dp [ abs ( x - tx )][ abs ( y - ty )] = min ( getsteps ( x1 y1 tx ty ) getsteps ( x2 y2 tx ty )) + 1 ; # exchanging the coordinates x with y of both # knight and target will result in same ans. dp [ abs ( y - ty )][ abs ( x - tx )] = dp [ abs ( x - tx )][ abs ( y - ty )]; return dp [ abs ( x - tx )][ abs ( y - ty )]; # Driver Code if __name__ == '__main__' : # size of chess board n*n n = 100 ; # (x y) coordinate of the knight. # (tx ty) coordinate of the target position. x = 4 ; y = 5 ; tx = 1 ; ty = 1 ; # (Exception) these are the four corner points # for which the minimum steps is 4. if (( x == 1 and y == 1 and tx == 2 and ty == 2 ) or ( x == 2 and y == 2 and tx == 1 and ty == 1 )): ans = 4 ; elif (( x == 1 and y == n and tx == 2 and ty == n - 1 ) or ( x == 2 and y == n - 1 and tx == 1 and ty == n )): ans = 4 ; elif (( x == n and y == 1 and tx == n - 1 and ty == 2 ) or ( x == n - 1 and y == 2 and tx == n and ty == 1 )): ans = 4 ; elif (( x == n and y == n and tx == n - 1 and ty == n - 1 ) or ( x == n - 1 and y == n - 1 and tx == n and ty == n )): ans = 4 ; else : # dp[a][b] here a b is the difference of # x & tx and y & ty respectively. dp [ 1 ][ 0 ] = 3 ; dp [ 0 ][ 1 ] = 3 ; dp [ 1 ][ 1 ] = 2 ; dp [ 2 ][ 0 ] = 2 ; dp [ 0 ][ 2 ] = 2 ; dp [ 2 ][ 1 ] = 1 ; dp [ 1 ][ 2 ] = 1 ; ans = getsteps ( x y tx ty ); print ( ans ); # This code is contributed by PrinciRaj1992
C# // C# code for minimum steps for // a knight to reach target position using System ; public class GFG { // initializing the matrix. static int [ ] dp = new int [ 8 8 ]; static int getsteps ( int x int y int tx int ty ) { // if knight is on the target // position return 0. if ( x == tx && y == ty ) { return dp [ 0 0 ]; } else // if already calculated then return // that value. Taking Absolute difference. if ( dp [ Math . Abs ( x - tx ) Math . Abs ( y - ty )] != 0 ) { return dp [ Math . Abs ( x - tx ) Math . Abs ( y - ty )]; } else { // there will be two distinct positions // from the knight towards a target. // if the target is in same row or column // as of knight then there can be four // positions towards the target but in that // two would be the same and the other two // would be the same. int x1 y1 x2 y2 ; // (x1 y1) and (x2 y2) are two positions. // these can be different according to situation. // From position of knight the chess board can be // divided into four blocks i.e.. N-E E-S S-W W-N . if ( x <= tx ) { if ( y <= ty ) { x1 = x + 2 ; y1 = y + 1 ; x2 = x + 1 ; y2 = y + 2 ; } else { x1 = x + 2 ; y1 = y - 1 ; x2 = x + 1 ; y2 = y - 2 ; } } else if ( y <= ty ) { x1 = x - 2 ; y1 = y + 1 ; x2 = x - 1 ; y2 = y + 2 ; } else { x1 = x - 2 ; y1 = y - 1 ; x2 = x - 1 ; y2 = y - 2 ; } // ans will be 1 + minimum of steps // required from (x1 y1) and (x2 y2). dp [ Math . Abs ( x - tx ) Math . Abs ( y - ty )] = Math . Min ( getsteps ( x1 y1 tx ty ) getsteps ( x2 y2 tx ty )) + 1 ; // exchanging the coordinates x with y of both // knight and target will result in same ans. dp [ Math . Abs ( y - ty ) Math . Abs ( x - tx )] = dp [ Math . Abs ( x - tx ) Math . Abs ( y - ty )]; return dp [ Math . Abs ( x - tx ) Math . Abs ( y - ty )]; } } // Driver Code static public void Main () { int i n x y tx ty ans ; // size of chess board n*n n = 100 ; // (x y) coordinate of the knight. // (tx ty) coordinate of the target position. x = 4 ; y = 5 ; tx = 1 ; ty = 1 ; // (Exception) these are the four corner points // for which the minimum steps is 4. if (( x == 1 && y == 1 && tx == 2 && ty == 2 ) || ( x == 2 && y == 2 && tx == 1 && ty == 1 )) { ans = 4 ; } else if (( x == 1 && y == n && tx == 2 && ty == n - 1 ) || ( x == 2 && y == n - 1 && tx == 1 && ty == n )) { ans = 4 ; } else if (( x == n && y == 1 && tx == n - 1 && ty == 2 ) || ( x == n - 1 && y == 2 && tx == n && ty == 1 )) { ans = 4 ; } else if (( x == n && y == n && tx == n - 1 && ty == n - 1 ) || ( x == n - 1 && y == n - 1 && tx == n && ty == n )) { ans = 4 ; } else { // dp[a b] here a b is the difference of // x & tx and y & ty respectively. dp [ 1 0 ] = 3 ; dp [ 0 1 ] = 3 ; dp [ 1 1 ] = 2 ; dp [ 2 0 ] = 2 ; dp [ 0 2 ] = 2 ; dp [ 2 1 ] = 1 ; dp [ 1 2 ] = 1 ; ans = getsteps ( x y tx ty ); } Console . WriteLine ( ans ); } } /*This code is contributed by PrinciRaj1992*/
JavaScript < script > // JavaScript code for minimum steps for // a knight to reach target position // initializing the matrix. let dp = new Array ( 8 ) for ( let i = 0 ; i < 8 ; i ++ ){ dp [ i ] = new Array ( 8 ). fill ( 0 ) } function getsteps ( x y tx ty ) { // if knight is on the target // position return 0. if ( x == tx && y == ty ) return dp [ 0 ][ 0 ]; else { // if already calculated then return // that value. Taking absolute difference. if ( dp [( Math . abs ( x - tx ))][( Math . abs ( y - ty ))] != 0 ) return dp [( Math . abs ( x - tx ))][( Math . abs ( y - ty ))]; else { // there will be two distinct positions // from the knight towards a target. // if the target is in same row or column // as of knight then there can be four // positions towards the target but in that // two would be the same and the other two // would be the same. let x1 y1 x2 y2 ; // (x1 y1) and (x2 y2) are two positions. // these can be different according to situation. // From position of knight the chess board can be // divided into four blocks i.e.. N-E E-S S-W W-N . if ( x <= tx ) { if ( y <= ty ) { x1 = x + 2 ; y1 = y + 1 ; x2 = x + 1 ; y2 = y + 2 ; } else { x1 = x + 2 ; y1 = y - 1 ; x2 = x + 1 ; y2 = y - 2 ; } } else { if ( y <= ty ) { x1 = x - 2 ; y1 = y + 1 ; x2 = x - 1 ; y2 = y + 2 ; } else { x1 = x - 2 ; y1 = y - 1 ; x2 = x - 1 ; y2 = y - 2 ; } } // ans will be 1 + minimum of steps // required from (x1 y1) and (x2 y2). dp [( Math . abs ( x - tx ))][( Math . abs ( y - ty ))] = Math . min ( getsteps ( x1 y1 tx ty ) getsteps ( x2 y2 tx ty )) + 1 ; // exchanging the coordinates x with y of both // knight and target will result in same ans. dp [( Math . abs ( y - ty ))][( Math . abs ( x - tx ))] = dp [( Math . abs ( x - tx ))][( Math . abs ( y - ty ))]; return dp [( Math . abs ( x - tx ))][( Math . abs ( y - ty ))]; } } } // Driver Code let i n x y tx ty ans ; // size of chess board n*n n = 100 ; // (x y) coordinate of the knight. // (tx ty) coordinate of the target position. x = 4 ; y = 5 ; tx = 1 ; ty = 1 ; // (Exception) these are the four corner points // for which the minimum steps is 4. if (( x == 1 && y == 1 && tx == 2 && ty == 2 ) || ( x == 2 && y == 2 && tx == 1 && ty == 1 )) ans = 4 ; else if (( x == 1 && y == n && tx == 2 && ty == n - 1 ) || ( x == 2 && y == n - 1 && tx == 1 && ty == n )) ans = 4 ; else if (( x == n && y == 1 && tx == n - 1 && ty == 2 ) || ( x == n - 1 && y == 2 && tx == n && ty == 1 )) ans = 4 ; else if (( x == n && y == n && tx == n - 1 && ty == n - 1 ) || ( x == n - 1 && y == n - 1 && tx == n && ty == n )) ans = 4 ; else { // dp[a][b] here a b is the difference of // x & tx and y & ty respectively. dp [ 1 ][ 0 ] = 3 ; dp [ 0 ][ 1 ] = 3 ; dp [ 1 ][ 1 ] = 2 ; dp [ 2 ][ 0 ] = 2 ; dp [ 0 ][ 2 ] = 2 ; dp [ 2 ][ 1 ] = 1 ; dp [ 1 ][ 2 ] = 1 ; ans = getsteps ( x y tx ty ); } document . write ( ans ' ' ); // This code is contributed by shinjanpatra. < /script>
الإخراج:
3
تعقيد الوقت: O(N * M) حيث N هو إجمالي عدد الصفوف وM هو إجمالي عدد الأعمدة
المساحة المساعدة: يا (ن * م)