0052. N-Queens II

https://leetcode.com/problems/n-queens-ii

Description

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

ac

https://leetcode.com/problems/n-queens-ii/discuss/20048/Easiest-Java-Solution-(1ms-98.22)

public class Solution {
    int count = 0;
    public int totalNQueens(int n) {
        boolean[] cols = new boolean[n];     // columns   |
        boolean[] d1 = new boolean[2 * n];   // diagonals \
        boolean[] d2 = new boolean[2 * n];   // diagonals /
        backtracking(0, cols, d1, d2, n);
        return count;
    }

    public void backtracking(int row, boolean[] cols, boolean[] d1, boolean []d2, int n) {
        if(row == n) count++;

        for(int col = 0; col < n; col++) {
            int id1 = col - row + n;
            int id2 = col + row;
            if(cols[col] || d1[id1] || d2[id2]) continue;

            cols[col] = true; d1[id1] = true; d2[id2] = true;
            backtracking(row + 1, cols, d1, d2, n);
            cols[col] = false; d1[id1] = false; d2[id2] = false;
        }
    }
}