<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:
    int n;
    bool isValid(vector<string>& curr, vector<int> col, vector<int> diag, vector<int> anti_diag, int r, int c){
        if(col[c])
            return false;
        if(diag[c-r + n-1])
            return false;
        if(anti_diag[r+c])
            return false;

        return true;

    }
    void solve(vector<vector<string>>& res, int r, vector<string>& curr, vector<int> col, vector<int> diag, vector<int> anti_diag){
        if(r == n){
            res.push_back(curr);
            return;
        }
        // bool res = false;
        for(int i=0; i<n; i++){
            curr[r][i] = 'Q';
            if(isValid(curr, col, diag, anti_diag, r, i)){
                col[i] = 1;
                diag[i-r+n-1] = 1;
                anti_diag[r+i] = 1;
                solve(res, r+1, curr, col, diag, anti_diag);
                col[i] = 0;
                diag[i-r+n-1] = 0;
                anti_diag[r+i] = 0;
            }
                
            curr[r][i] = '.';
            
        }
    }
    vector<vector<string>> solveNQueens(int a) {
        n = a;

        // vector<int> row(n);
        vector<int> col(n, 0);
        vector<int> diag(2*n-1, 0);
        vector<int> anti_diag(2*n-1, 0);

        vector<vector<string>> res;
        vector<string> curr(n, "");
        for(int i=0; i<n; i++){
            for(int j=0; j<n; j++)
                curr[i] = curr[i] + '.';
        }

        solve(res, 0, curr, col, diag, anti_diag);
    
        return res;
    }
};
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