#Modification 13

Author: amangit1314

backtracking/N_Queen.java

@@ -0,0 +1,86 @@
+package backtracking;
+
+public class N_Queen {
+    final int N = 4;
+
+    void printSolution(int board[][]) {
+        for (int i = 0; i < N; i++) {
+            for (int j = 0; j < N; j++) {
+                System.out.print(" " + board[i][j] + " ");
+                System.out.println();
+            }
+        }
+    }
+
+    boolean isSafe(int board[][], int row, int col) {
+        int i, j;
+
+        for (i = 0; i < col; i++) {
+            if (board[row][i] == 1)
+                return false;
+        }
+
+        for (i = row, j = col; i >= 0 && j >= 0; i--, j--) {
+            if (board[i][j] == 1) {
+                return false;
+            }
+        }
+
+        for (i = row, j = col; j >= 0 && i < N; i++, j--) {
+            if (board[i][j] == 1)
+                return false;
+        }
+
+        return true;
+    }
+
+    boolean solveNQUtil(int board[][], int col) {
+        if (col >= N)
+            return true;
+
+        for (int i = 0; i < N; i++) {
+            if (isSafe(board, i, col)) {
+                board[i][col] = 1;
+
+                if (solveNQUtil(board, col + 1) == true)
+                    return true;
+
+                /*
+                If placing queen in board[i][col] doesn't lead to a solution then rempve queen from board[i][col]
+                */
+                board[i][col] = 0;  //"BACKTRACK"
+            }
+        }
+
+        /*
+        * If the queen can not be palced in any row in this col, then return false
+        */
+        return false;
+    }
+    
+    /*
+    * This function solves the N-Queen problem using "BACKTRACKING".
+    * It mainly uses solveNQUtil() to solve the problem.
+    * It return false if queens cannot placed, otherwise, 
+    * return true & prints placement of queens in the form of 1's.  
+    * Please note that there may be more than one solutions, 
+    * this functionprints one of the feasible solutions. 
+    */
+    boolean solveNQ() {
+        int board[][] = { { 0, 0, 0, 0 }, { 0, 0, 0, 0 }, { 0, 0, 0, 0 }, { 0, 0, 0, 0 } };
+
+        if (solveNQUtil(board, 0) == false) {
+            System.out.println("Solution does not exist");
+            return false;
+        }
+
+        printSolution(board);
+        return true;
+    }
+
+        //Driver program to test above functions
+        public static void main(String[] args) {
+        N_Queen nq = new N_Queen();
+        nq.solveNQ();
+    }
+}