<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:
    vector<vector<string>> finalAns;

    bool canBePlaced(vector<string>&ans,int srow,int scol,int erow)
    {
        for(int i=0;i<srow;i++)
        {
            if(ans[i][scol]=='Q') return false;
        }
        for(int i=srow-1,j=scol-1;i>=0&&j>=0;i--,j--)
        {
            if(ans[i][j]=='Q') return false;
        }
        for(int i=srow-1,j=scol+1;i>=0&&j<erow;i--,j++)
        {
            if(ans[i][j]=='Q') return false;
        }
        return true;
    }


    void solve(vector<string> ans,int srow,int erow)
    {
        if(srow==erow)
        {
            finalAns.push_back(ans);
            return;
        } 
        for(int i=0;i<erow;i++)
        {
            ans[srow][i]='Q';
            if(canBePlaced(ans,srow,i,erow)) solve(ans,srow+1,erow);
            ans[srow][i]='.';
        }

    }
    vector<vector<string>> solveNQueens(int n) {
        
        vector<string> ans(n);
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<n;j++)
            {
                ans[i]+=".";
            }
        }
        solve(ans,0,n);
        

        return finalAns;


    }
};
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