Find Longest Awesome Substring
<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>
Bit Manipulation; Hash Table; String
class Solution {
public:
    int longestAwesome(string s) {
        vector<int> d(1024, -1);
        d[0] = 0;
        int st = 0, ans = 1;
        for (int i = 1; i <= s.size(); ++i) {
            int v = s[i - 1] - '0';
            st ^= 1 << v;
            if (~d[st]) {
                ans = max(ans, i - d[st]);
            } else {
                d[st] = i;
            }
            for (v = 0; v < 10; ++v) {
                if (~d[st ^ (1 << v)]) {
                    ans = max(ans, i - d[st ^ (1 << v)]);
                }
            }
        }
        return ans;
    }
};