Create NKnights.java

This is a Java Program to find all the possible combinations to place N Knights in an NxN Chessboard such that they all are non-attacking to each other.

algorithms/Java/backtracking/NKnights.java

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+public class NKnights {
+    public static void main(String[] args) {
+        int n=3;
+        boolean[][] board=new boolean[n][n];
+        System.out.println(2*knight(board,0,0,3));
+    }
+    static int knight(boolean[][] board,int row,int col,int tar){
+        if(tar==0){
+            display(board);
+            System.out.println();
+            return 1;
+        }
+        int count=0;
+        if(row==board.length-1 && col==board.length) {
+            return 1;
+        }
+        if(col== board.length){
+            count+= knight(board,row+1,0,tar);
+            return 1;
+        }
+        if(isSafe(board,row,col)){
+            board[row][col]=true;
+            count+=knight(board,row,col+1,tar-1);
+            board[row][col]=false;
+        }
+
+        count+=knight(board,row,col+1,tar);
+        return count;
+    }
+
+    private static boolean isSafe(boolean[][] board, int row, int col) {
+        if(isValid(board, row-2, col-1)){
+            if(board[row-2][col-1]){
+                return false;
+            }
+        }
+        if(isValid(board, row-1, col-2)){
+            if(board[row-1][col-2]){
+                return false;
+            }
+        }
+        if(isValid(board, row-2, col+1)){
+            if(board[row-2][col+1]){
+                return false;
+            }
+        }
+        if(isValid(board, row-1, col+2)){
+            if(board[row-1][col+2]){
+                return false;
+            }
+        }
+        return true;
+    }
+    // TO CHECK THE BOUNDARIES OF ROWS AND COLUMNS
+    static boolean isValid(boolean[][] board,int row,int col){
+        if(row>=0 && row<board.length && col>=0 && col<board.length){
+            return true;
+        }
+        return false;
+    }
+
+    private static void display(boolean[][] board) {
+        for(boolean[] row: board){
+            for(boolean element:row){
+                if(element){
+                    System.out.print("K ");
+                }
+                else{
+                    System.out.print(". ");
+                }
+            }
+            System.out.println();
+        }
+    }
+}