<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>the number of distinct solutions to the&nbsp;<strong>n-queens puzzle</strong></em>.</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> 2
<strong>Explanation:</strong> There are two distinct solutions to the 4-queens puzzle as shown.
</pre>

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

<pre>
<strong>Input:</strong> n = 1
<strong>Output:</strong> 1
</pre>

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

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

class Solution {
public:
int ans = 0;
int N;

void bc(int row, set<int> c, set<int> d1, set<int> d2) {
    if (row==N){
        ans++;
        return;
    }
    for (int col = 0; col < N;col++) {
        if (!c.contains(col) && !d1.contains(row-col) && !d2.contains(N-col-row)) {
            c.insert(col);
            d1.insert(row-col);
            d2.insert(N-col-row);
            bc(row+1, c, d1, d2);
            c.erase(col);
            d1.erase(row-col);
            d2.erase(N-row-col);
        }
    }
}

    int totalNQueens(int n) {
        N= n;
        bc(0, {}, {}, {});
        return ans;

    }
};
27957