<p>You are given a string <code>s</code>. An <strong>awesome</strong> substring is a non-empty substring of <code>s</code> such that we can make any number of swaps in order to make it a palindrome.</p>

<p>Return <em>the length of the maximum length <strong>awesome substring</strong> of</em> <code>s</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;3242415&quot;
<strong>Output:</strong> 5
<strong>Explanation:</strong> &quot;24241&quot; is the longest awesome substring, we can form the palindrome &quot;24142&quot; with some swaps.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;12345678&quot;
<strong>Output:</strong> 1
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;213123&quot;
<strong>Output:</strong> 6
<strong>Explanation:</strong> &quot;213123&quot; is the longest awesome substring, we can form the palindrome &quot;231132&quot; with some swaps.
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>5</sup></code></li>
	<li><code>s</code> consists only of digits.</li>
</ul>

class Solution {
public:
    int longestAwesome(string s) {

        int n = s.size();
        vector<int> msk(1024, n);
        msk[0]=-1;
        int ln = 0, mask = 0;
        for (int i = 0; i < n; i++) {
             mask ^= (1 << (s[i] - '0'));
            // check even palindrome
            if (mask == 0)
                ln = i + 1;
            
            ln = max(ln, i - msk[mask]);

            // check odd palindrome
            for (int j = 0; j < 10; j++) {
                int nmask_again;

                nmask_again = mask ^ (1 << j);
                ln = max(ln, i - msk[nmask_again]);
            }
            msk[mask] = min(msk[mask], i);
        }

        return ln;
    }
};
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