[LeetCode]N-Queens II

N-Queens II

Follow up for N-Queens problem.

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

 

和上题N-Queens几乎一样，还简单点。

class Solution {
private:
  int res;
public:
  int totalNQueens(int n) {
    vector<int> state(n, -1);
    res = 0;
    helper(state, 0);
    return res;
  }
  void helper(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;
        helper(state, row+1);
        state[row] = -1;
      }
  }
  bool isValid(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;
  }

};