生成N皇后问题所有局面 N-Queens

Backtracking is a general algorithm for finding all (or some) solutions to some computational problem, that incrementally builds candidates to the solutions, and abandons each partial candidate c ("backtracks") as soon as it determines that c cannot possibly be completed to a valid solution.

代码：

class Solution {
public:
    vector<vector<string> > boards; //所有盘面的集合

    vector<vector<string> > solveNQueens(int n) {
        boards.clear();
        if(n == 0)
            return boards;

        int A[n];
        memset(A, 0, sizeof(A));
        queen(A, n, 0);
        return boards;
    }

    void queen(int A[], int n, int row) //Backtrack
    {
        if(row == n)
        {
            boards.push_back(addone(A, n));
        }
        else
        {
            for(int i=0;i<n;i++)
                if(isValid(A, n, row, i))
                {
                    A[row] = i;
                    queen(A, n, row+1);
                }
        }
    }

    bool isValid(int A[], int n, int row, int col) //判定冲突
    {
        for(int i=0;i<row;i++)
        {
            if(A[i] == col)
                return false;
            if(abs(A[i] - col) == abs(i - row))
                return false;
        }
        return true;
    }

    vector<string> addone(int A[], int n) //由一维数组形式生成盘面
    {
        vector<string> one;
        for(int i=0;i<n;i++)
        {
            string tmp = "";
            for(int j=0;j<n;j++)
                if(A[i] != j)
                    tmp += '.';
                else
                    tmp += 'Q';

            one.push_back(tmp);
        }
        return one;
    }

};