Leetcode 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) {
vector<int> queen(n,0);
for(int i = 0 ; i < n; ++ i) queen[i] = i;
int cnt = 0;
do{
bool flag = false;
for(int i = 1; i < n && !flag; ++ i){
for(int j = 0 ; j < i && !flag ; ++ j){
if(abs(i-j) == abs(queen[i]-queen[j])) flag=true;
}
}
if(!flag) cnt++;
}while(next_permutation(queen.begin(),queen.end()));
return cnt;
}
};