<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 {
private:
    bool inDiag(vector<string> curr, int x, int y, int n){
        // printf("Checking diag for (%d, %d)\n", x, y);
        for(int i=x-min(x,y), j=y-min(x,y); i<n&&j<n; i++, j++){
            if(curr[i][j] == 'Q')
                return true;
        }

        int maxAdd = min(x, n-1-y);

        for(int i=x-maxAdd, j=y+maxAdd; i<n && j>=0; i++, j--){
            if(curr[i][j] == 'Q')
                return true;
        }

        return false;
    }

    void printer(vector<string>& arr){
        for(int i=0; i<arr.size(); i++){
            for(int j=0; j<arr[0].size(); j++)
                cout << arr[i][j] << " ";
            cout << endl;
        }
    }

    void go(int queenCount, vector<vector<string>>& ans, vector<string>& curr, int& n, unordered_set<int>& inRow, int j){
        if(queenCount == 0){
            // printf("Below config worked!\n");
            // printer(curr);
            ans.push_back(curr);
        }

        for(int i=0; i<n; i++){
            if(inRow.find(i) != inRow.end() || inDiag(curr, i, j, n))
                continue;
            curr[i][j] = 'Q';
            inRow.insert(i);

            // printf("Placed queen at (%d, %d)\n", i, j);
            go(queenCount-1, ans, curr, n, inRow, j+1);
            // printf("Removing queen from (%d, %d)\n", i, j);
            curr[i][j] = '.';
            inRow.erase(i);
        }
    }

    string create(int& n){
        string ret = "";
        for(int i=0; i<n; i++)
            ret += '.';
        return ret;
    }
public:
    vector<vector<string>> solveNQueens(int n) {
        vector<vector<string>> ans;
        vector<string> curr (n, string(n, '.'));
        unordered_set<int> inRow, inCol;
        
        go(n, ans, curr, n, inRow, 0);
        return ans;
    }
};
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