N-Queens II

Follow up for N-Queens problem.

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

 

#include<iostream>

#include<vector>

#include<cmath>

using namespace std;



class Solution

{

public:

    int res=0;

    int totalNQueens(int n)

    {



        vector<int> state(n,-1);

        helper(n,0,state);

        return res;

    }

    void helper(int n,int start,vector<int> &state)

    {

        if(start==n)

        {

            res++;

            return;

        }

        int i;

        for(i=0; i<n; i++)

        {

            if(isValid(state,start,i))

            {

                state[start]=i;

                helper(n,start+1,state);

                state[start]=-1;

            }

        }

    }

    bool isValid(vector<int> &state,int row,int col)

    {

        int i;

        for(i=0; i<row; i++)

            if(state[i]==col||row-i==abs(state[i]-col))

                return false;

        return true;

    }

};



int main()

{

    Solution s;

    cout<<s.totalNQueens(4)<<endl;

}