<p>The <strong>n-queens</strong> puzzle is the problem of placing <code>n</code> queens on an <code>n x n</code> chessboard such that no two queens attack each other.</p>

<p>Given an integer <code>n</code>, return <em>all distinct solutions to the <strong>n-queens puzzle</strong></em>. You may return the answer in <strong>any order</strong>.</p>

<p>Each solution contains a distinct board configuration of the n-queens&#39; placement, where <code>&#39;Q&#39;</code> and <code>&#39;.&#39;</code> both indicate a queen and an empty space, respectively.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/11/13/queens.jpg" style="width: 600px; height: 268px;" />
<pre>
<strong>Input:</strong> n = 4
<strong>Output:</strong> [[&quot;.Q..&quot;,&quot;...Q&quot;,&quot;Q...&quot;,&quot;..Q.&quot;],[&quot;..Q.&quot;,&quot;Q...&quot;,&quot;...Q&quot;,&quot;.Q..&quot;]]
<strong>Explanation:</strong> There exist two distinct solutions to the 4-queens puzzle as shown above
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 1
<strong>Output:</strong> [[&quot;Q&quot;]]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 9</code></li>
</ul>

class Solution {
public:
    unordered_map<int,bool> rows;
    unordered_map<int,bool> lowerdiagonal;
    unordered_map<int,bool> upperdiagonal;
    bool isSafe(vector<vector<char>> & board,int row ,int col,int n)
    {
        if(rows[row]==true || lowerdiagonal[row+col]==true || upperdiagonal[row-col]==true)
            return false;    
        return true;

    }
    vector<vector<string>> storesolution(vector<vector<char>> & board,vector<vector<string>> & ans,int n)
    {
        vector<string> tempans;
        for(int i=0;i<n;i++)
        {
            string output="";
            for(int j=0;j<n;j++)
            {
                output.push_back(board[i][j]);
            }
            tempans.push_back(output);
        }
        ans.push_back(tempans);
        return ans;
    }
    void placer(vector<vector<char>> & board,vector<vector<string>> &ans,int col,int n)
    {
        if(col>=n)
        {
            storesolution(board,ans,n);
            return;
        }
        for(int row=0;row<board.size();row++)
        {
            if(isSafe(board,row,col,n))
            {
                board[row][col]='Q';
                rows[row]=true;
                lowerdiagonal[row+col]=true;
                upperdiagonal[row-col]=true;           
                placer(board,ans,col+1,n);
                rows[row]=false;
                lowerdiagonal[row+col]=false;
                upperdiagonal[row-col]=false;
                board[row][col]='.';
            }
        }
    }
    vector<vector<string>> solveNQueens(int n) 
    {
        vector<vector<char>>board(n,vector<char>(n,'.'));
        vector<vector<string>>ans;
        placer(board,ans,0,n);    
        return ans;
    }
};
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