LeetCode: N-Queens

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.."]
]

递归解法：

class Solution {
public:
    bool check(int row, int* place)  
    {  
        for (int i = 0; i < row; ++i)  
        {  
            int diff = abs(place[i] - place[row]);  
            if (diff == 0 || diff == row - i)  
                return false;  
        }  
        return true;  
    }  
      
    void placeQueens(int row, int n, int &count, int* place,
                     vector<vector<string> > &result)  
    {  
        if (row == n)  
        {
            vector<string> tmp;
            for (int i = 0; i < row; ++i)
            {
                string str(n, '.');
                str[place[i]] = 'Q';
                tmp.push_back(str);
            }
            result.push_back(tmp);
            return;  
        }  
          
        for (int i = 0; i < n; ++i)  
        {  
            place[row] = i;  
            if (check(row, place))  
                placeQueens(row+1, n, count, place, result);  
        }  
    }  
    vector<vector<string> > solveNQueens(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int* place = new int[n];  
        int count = 0;  
        vector<vector<string> > result;
        placeQueens(0, n, count, place, result); 
        return result;
    }
};