leetcode - N-Queens II

Follow up for N-Queens problem.

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

class Solution {
private:
int res;
public:
int totalNQueens(int n) {
std::vector<int> state(n, -1);
res = 0;
dfs(state, 0);
return res;
}
void dfs(std::vector<int> &state, int row)
{
int n = state.size();
if(row == n)
{
res++;
return;
}
for(int col = 0; col < n; col++)
if(isValid(state, row, col))
{
state[row] = col;
dfs(state, row+1);
state[row] = -1;;
}
}
bool isValid(std::vector<int> &state, int row, int col)
{
for(int i = 0; i < row; i++)
if(state[i] == col || abs(row - i) == abs(col - state[i]))
return false;
return true;
}

};