LeetCode – Refresh – N-Queens II

You can use N-Queens I 's method counting for the result. But it wont pass the leetcode test.

Use bit operation will be much faster:

class Solution {
private:
    int count, rec;
public:
    void getQueen(int row, int ld, int rd) {
        if (row == rec) {
            count++;
            return;
        } else {
            int nonOccupied = rec & ~(row | rd | ld), occupy;
            while (nonOccupied != 0) {
                occupy = nonOccupied & (~nonOccupied + 1);
                nonOccupied -= occupy;
                getQueen(row + occupy, (ld + occupy) << 1, (rd + occupy) >> 1);
            }
        }
    }
    int totalNQueens(int n) {
        count = 0;
        rec = (1 << n) - 1;
        getQueen(0, 0, 0);
        return count;
    }
};