N-Queens II

代码：

    int result;
    void search(int line, int total, vector<bool> &col, vector<bool> &left, vector<bool> &right){
        if(line == total){
            result++;
            return;
        }
        int i;
        for(i = 0; i < total; i++){
            if(col[i] && left[line+i] && right[line+total-i-1]){
                col[i] = false;
                left[line+i] = false;
                right[line+total-i-1] = false;
                search(line+1, total, col, left, right);
                col[i] = true;
                left[line+i] = true;
                right[line+total-i-1] = true;
            }
        }
    }
    int totalNQueens(int n) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        result=0;
        vector<bool> col(n, true), left(2*n-1, true), right(2*n-1, true);
        search(0, n, col, left, right);
        return result;
    }