counts total possible way to place N Queens in NXN board, backtracking, recursion

Author: NirmalSilwal

CodingBlocks Training/Day12/NQueen.java

@@ -0,0 +1,65 @@
+package Lecture12;
+
+public class NQueen {
+
+	public static void main(String[] args) {
+		
+		int N = 4;
+		boolean[][] board = new boolean[N][N];
+		int row = 0;
+		System.out.println(countNQueens(board, row));	// 2
+	}
+
+	public static int countNQueens(boolean[][] board, int row) {
+		if (row == board.length) {
+			return 1;
+		}
+
+		int count = 0;
+		for (int col = 0; col < board.length; col++) {
+			if (isSafePosition(board, row, col)) {
+				board[row][col] = true;
+				count = count + countNQueens(board, row + 1);
+				board[row][col] = false;
+			}
+		}
+		return count;
+	}
+
+	public static boolean isSafePosition(boolean[][] board, int row, int col) {
+		// checking column
+		for (int i = row; i >= 0; i--) {
+			if (board[i][col]) {
+				return false;
+			}
+		}
+
+		// checking left diagonal
+		for (int i = row, j = col; i >= 0 && j >= 0; i--, j--) {
+			if (board[i][j]) {
+				return false;
+			}
+		}
+
+		// checking right diagonal
+		for (int i = row, j = col; i >= 0 && j < board.length; i--, j++) {
+			if (board[i][j]) {
+				return false;
+			}
+		}
+
+		return true;
+	}
+
+	/*
+	public static void display(boolean[][] board) {
+		for (int row = 0; row < board.length; row++) {
+			for (int col = 0; col < board[row].length; col++) {
+				System.out.print(board[row][col] + " ");
+			}
+			System.out.println();
+		}
+	}
+	*/
+	
+}