LeetCode 52. N-Queens II

Get the idea from this post: https://developers.google.com/optimization/puzzles/queens

We only to track three arrays. One is horizontally, one is vertically, one is diagonally.

Horizontally is main[2 * n  - 1], Vertically is col[n], diagonally is anti[2 * n - 1];

int totalNQueens(int n) {    vector<bool> col(n, true);    vector<bool> anti(2*n-1, true);    vector<bool> main(2*n-1, true);    int count = 0;    dfs(0, col, main, anti, count);    return count;}void dfs(int i, vector<bool> &col, vector<bool>& main, vector<bool> &anti, int &count) {        if (i == col.size()) {            count++;            return;        }       for (int j = 0; j < col.size(); j++) {         if (col[j] && main[i+j] && anti[i+col.size()-1-j]) {             col[j] = main[i+j] = anti[i+col.size()-1-j] = false;             dfs(i+1, col, main, anti, count);             col[j] = main[i+j] = anti[i+col.size()-1-j] = true;      }    }}