leetcode:N-Queens II

Follow up for N-Queens problem.

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

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这题的思想和数独是一样的，看一下这个position（数）是否是valid，如果valid就继续往下走一步

class Solution {    private:    bool isValidPosition(int curRow, int tryColoum, vector<int> &auxVtr) {                for (int i=0; i<=curRow; i++)        {            if (auxVtr[i] == tryColoum)                return false;                            if (abs(curRow-i) == abs(tryColoum-auxVtr[i]))                return false;        }                return true;    }    void NQueensHelper(int curRow, int totalNum, vector<int> &auxVtr, int &retVal) {           if (curRow == totalNum)        {            retVal++;            return;        }                for (int tryColoum = 0; tryColoum<totalNum; tryColoum++)        {            if (isValidPosition(curRow, tryColoum, auxVtr))            {                auxVtr[curRow] = tryColoum;                NQueensHelper(curRow+1, totalNum, auxVtr, retVal);                auxVtr[curRow] = -1;            }        }    }    public:    int totalNQueens(int n) {                int retVal = 0;                vector<int> auxVtr(n, -1);                NQueensHelper(0, n, auxVtr, retVal);                return retVal;    }};