leetcode[51]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.."]

]

class Solution {

public:

void init(vector<string> &temp, int n)

{

    string strtemp(n,'.');

    temp.insert(temp.end(),n,strtemp);

    return;

}

bool checkij(vector<string> &temp, int i, int j)

{

    for (int ii=i-1,jleft=j-1;ii>=0&&jleft>=0;ii--,jleft--)

    {

        if(temp[ii][jleft]=='Q')return false;

    }

    for (int ii=i-1,jright=j+1;ii>=0&&jright<temp.size();ii--,jright++)

    {

        if(temp[ii][jright]=='Q')return false;

    }

    for (int k=0;k<temp.size();k++)

    {

        if (k!=j&&temp[i][k]=='Q')return false;

        if (k!=i&&temp[k][j]=='Q')return false;

    }

    return true;

}

bool solveOne(vector<vector<string>> &res,vector<string> &temp,int n, int index)

{

    if(index==n)

    {

        res.push_back(temp);

        return true;

    }

    for (int j=0;j<n;j++)

    {

        temp[index][j]='Q';

        if (checkij(temp,index,j))

        {

            solveOne(res,temp,n,index+1);

        }

        temp[index][j]='.';    

    }

}

vector<vector<string>> solveNQueens(int n) 

{

    vector<vector<string>> res;

    vector<string> temp;

    init(temp,n);

    for(int i = 0; i < n; i++) {

        temp[0][i] = 'Q';

        solveOne(res, temp, n, 1);

        temp[0][i] = '.';

    }

    return res;

}

};