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:
    vector<vector< string> > solveNQueens( int n) 
    {
        vector<vector< string>> result;
         if(n== 0)  return result;
         int loc[n];
        generate(result,loc,n, 0);
         return result;
    }
     void generate(vector<vector< string>>& result, int* loc, int n, int row)
    {
         if(row==n)
        {
            vector< string> v;
             for( int i= 0;i<n;i++)
            {
                 string s;
                 for( int j= 0;j<n;j++) s=s+ " . ";
                s[loc[i]]= ' Q ';
                v.push_back(s);
            }
            result.push_back(v);
             return;
        }
         for( int i= 0;i<n;i++)
        {
             int j;
             for(j= 0;j<row;j++)
                 if(loc[j]==i || row-j==loc[j]-i || row-j==i-loc[j])
                     break;
             if(j==row)
            {
                loc[row]=i;
                generate(result,loc,n,row+ 1);
            }
        }
    }
};