[leetcode 52] N-Queens II

Follow up for N-Queens problem.

Now, instead outputting board configurations, return the total number of distinct solutions.

class Solution {
public:
    int totalNQueens(int n) {
        this->res = 0;
        this->col = vector<int>(n,0);  
        this->main_diag = vector<int>(2*n,0);  
        this->anti_diag = vector<int>(2*n,0);
        vector<int> path(n,0);
        dfs(path, 0);
        return this->res;
    }
private:
    int res;
    vector<int> col;
    vector<int> main_diag;
    vector<int> anti_diag;
    void dfs(vector<int> &path, int row) {
        const int N = path.size();
        if (row == N) {
            ++this->res;
            return;
        }
        for (int i = 0; i < N; i++) {
            bool ok = col[i] == 0 && main_diag[row+i]==0 && anti_diag[row-i+N]==0;
            if(!ok) {
                continue;
            }
            path[row] = i;
            col[i] = main_diag[row+i]= anti_diag[row-i+N]= 1;
            dfs(path,row+1);
            col[i] = main_diag[row+i]= anti_diag[row-i+N]= 0;
        }
    }
    
};