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
;
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);
}
}
}
};