N-Queens II

Follow up for N-Queens problem.

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

class Solution {
public:
    bool isValid(vector<string>& svec, int i, int j, int n)
    {
        for(int h = 0; h < j; ++h)
        {
            if(svec[i][h] == 'Q')
            {
                return false;
            }
        }
        for(int k = 0; k < i; ++k)
        {
            if(svec[k][j] == 'Q')
            {
                return false;
            }
        }

        int k = i - 1, h = j - 1;
        while(k >= 0 && h >= 0)
        {
            if(svec[k][h] == 'Q')
            {
                return false;
            }
            k--;
            h--;
        }

        k = i + 1;
        h = j + 1;
        while(k < n && h < n)
        {
            if(svec[k][h] == 'Q')
            {
                return false;
            }
            ++k;
            ++h;
        }

        k = i - 1, h = j + 1;
        while(k >= 0 && h < n)
        {
            if(svec[k][h] == 'Q')
            {
                return false;
            }
            --k;
            h++;
        }

        k = i + 1, h = j - 1;
        while(k < n && h >= 0)
        {
            if(svec[k][h] == 'Q')
            {
                return false;
            }
            ++k;
            --h;  
        }
        return true;
    }
    void help(vector<string>& svec, int dep, int n, int& sum)
    {
        if(dep == n)
        {
            //vsvec.push_back(svec);
            ++sum;
            return;
        }
        for(int i = 0; i < n; ++i)
        {
            if(isValid(svec, i, dep, n))
            {
                svec[i][dep] = 'Q';
                help(svec, dep + 1, n, sum);
                svec[i][dep] = '.';
            }

        }
    }
    int totalNQueens(int n)
    {
        if(n <= 0)
        {
            return 0;
        }
        string s = "";
        for(int i = 0; i < n; ++i)
        {
            s += '.';
        }
        vector<string> svec(n, s);
        int sum = 0;
        help(svec, 0, n, sum);
        return sum;
    }
};