LeetCode-52. N-Queens II [C++][Java]

LeetCode-52. N-Queens IIhttps://leetcode.com/problems/n-queens-ii/

The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other.

Given an integer n, return the number of distinct solutions to the n-queens puzzle.

Example 1:

Input: n = 4
Output: 2
Explanation: There are two distinct solutions to the 4-queens puzzle as shown.

Example 2:

Input: n = 1
Output: 1

Constraints:

1 <= n <= 9

class Solution {
public:
    int totalNQueens(int n) {
        if (n == 0) {return 0;}
        vector board(n, string(n, '.'));
        vector column(n, false), ldiag(2*n-1, false), rdiag(2*n-1, false);
        return backtracking(board, column, ldiag, rdiag, 0, n);
    }
    
    int backtracking(vector& board,
                      vector& column, vector& ldiag, vector& rdiag,
                      int row, int n) {
        if (row == n) {
            return 1;
        }
        int count = 0;
        for (int i = 0; i < n; i++) {
            if (column[i] || ldiag[n-1-row+i] || rdiag[row+i]) {
                continue;
            }
            board[row][i] = 'Q';
            column[i] = ldiag[n-1-row+i] = rdiag[row+i] = true;
            count += backtracking(board, column, ldiag, rdiag, row + 1, n);
            board[row][i] = '.';
            column[i] = ldiag[n-1-row+i] = rdiag[row+i] = false;
        }
        return count;
    }
};

class Solution {
    public int totalNQueens(int n) {
        if (n == 0) {return 0;}
        char[][] board = initBoard(n);
        boolean[] column = new boolean[n];
        boolean[] ldiag = new boolean[2*n-1];
        boolean[] rdiag = new boolean[2*n-1];
        return backtracking(board, column, ldiag, rdiag, 0, n);
    }
    
    private char[][] initBoard(int n) {
        char[][] board = new char[n][n];
        for (char[] str: board) {Arrays.fill(str, '.');}
        return board;
    }
    
    int backtracking(char[][] board,
                      boolean[] column, boolean[] ldiag, boolean[] rdiag,
                      int row, int n) {
        if (row == n) {
            return 1;
        }
        int count = 0;
        for (int i = 0; i < n; i++) {
            if (column[i] || ldiag[n-1-row+i] || rdiag[row+i]) {
                continue;
            }
            board[row][i] = 'Q';
            column[i] = ldiag[n-1-row+i] = rdiag[row+i] = true;
            count += backtracking(board, column, ldiag, rdiag, row + 1, n);
            board[row][i] = '.';
            column[i] = ldiag[n-1-row+i] = rdiag[row+i] = false;
        }
        return count;
    }
}