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;
}
};```