【leetcode】NQueens

Question：

The n-queens puzzle is the problem of placing n queens on an n*n chessboard such that no two queens attack each other.

Given an integer n, return all distinct solutions to the n-queens puzzle.

Each solution contains a distinct board configuration of the n-queens' placement, where 'Q' and '.' both indicate a queen and an empty space respectively.

For example,
There exist two distinct solutions to the 4-queens puzzle:

[
 [".Q..",  // Solution 1
  "...Q",
  "Q...",
  "..Q."],

 ["..Q.",  // Solution 2
  "Q...",
  "...Q",
  ".Q.."]
]

Anwser 1：      

class Solution {
public:
    bool check(int row, int* colArray) {
        for (int i = 0; i < row; ++i) 
        {
            int diff = abs(colArray[i] - colArray[row]);      // in a col
            if (diff == 0 || diff == row - i) {         // int a row or line
                return false;
            }
        }
        return true;
    }
    
    void placeQueens(int row, int n, int &count, int* colArray, vector< vector<string> > &ret2) {
        if (row == n) {
            ++count;
            
            vector<string> tmpRet;
            for(int i = 0; i < row; i++){
                string str(n, '.');
                str[colArray[i]] = 'Q';
                tmpRet.push_back(str);
            }
            ret2.push_back(tmpRet);
            return;
        }
        
        for (int col = 0; col < n; ++col) {     // in 0 row, test n col
            colArray[row] = col;
            if (check(row, colArray)){
                placeQueens(row+1, n, count, colArray, ret2);    // test other rows
            }
        }
    }
    
    vector<vector<string> > solveNQueens(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int *colArray = new int[n];
        int count = 0;
        
        
        vector< vector<string> > ret;
        placeQueens(0, n, count, colArray, ret);
        
        return ret;
    }
};