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Author: shatakshigarg

N QUEENS.txt

@@ -0,0 +1,83 @@
+public class Solution {
+	
+		
+public static void placeNQueens(int n){
+		
+	/* Your class should be named Solution.
+	 * Don't write main() function.
+	 * Don't read input, it is passed as function argument.
+	 * Print output as specified in the question
+	 */
+	int[][] board = new int[n][n];
+    solveNQueens(board, 0,n); 
+
+	}
+    
+    static void solveNQueens(int board[][], int row, int N) 
+	{ 
+    /* base case: If all queens are placed 
+    then return true */
+    if (row == N) 
+    { 
+        printSolution(board,N); 
+        return;
+    } 
+ 
+    /* Consider this column and try placing 
+    this queen in all rows one by one */
+    for (int i = 0; i < N; i++) 
+    { 
+        /* Check if queen can be placed on 
+        board[row][i] */
+        if ( isSafe(board, row, i, N) ) 
+        { 
+            /* Place this queen in board[row][i] */
+            board[row][i] = 1; 
+ 
+            // Make result true if any placement 
+            // is possible 
+            solveNQueens(board, row + 1, N); 
+ 
+            /* If placing queen in board[row][i] 
+            doesn't lead to a solution, then backtrack and
+            remove queen from board[row][i] */
+            board[row][i] = 0; 
+        } 
+    } 
+
+	}
+    
+    static boolean isSafe(int board[][], int row, int col, int N) 
+	{ 
+    int i, j; 
+        
+    //Check if all values in the given column and rows from 0 to row-1 are 0
+    for (i=0;i<row;i++)
+    {
+        if (board[i][col]==1)
+            return false;
+    }
+        
+	// Check upper diagonal on left side
+    for (i = row, j = col; i >= 0 && j >= 0; i--, j--) 
+        if (board[i][j] == 1) 
+            return false;
+        
+	//Check upper right diagonal
+    for (i=row,j=col;i>=0 && j<N;i--,j++)
+        if (board[i][j] == 1) 
+            return false;
+ 
+    return true; 
+	} 
+    
+    static void printSolution(int board[][], int N) 
+	{ 
+    for (int i = 0; i < N; i++) 
+    { 
+        for (int j = 0; j < N; j++) 
+            System.out.print(board[i][j]+" ");  
+    } 
+    System.out.println(); 
+	} 
+}