<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) {
        unordered_map<int,int> map; // presum to index
        map[0] = -1;
        int presum = 0;
        int n = s.size();
        int res = 0;
        for (int i = 0; i < n ; i++) {
            presum = presum ^ (1 << (s[i] - '0'));
            if (map.count(presum)) {
                res = max(res, i - map[presum]);
            }
            // one diff
            for (int j = 0; j <= 9; j++) {
                int oneDiff = presum ^ (1 << j);
                if (map.count(oneDiff)) {
                    res = max(res, i - map[oneDiff]);
                }
            }
            if (!map.count(presum))
                map[presum] = i;
        }
        return res;
    }
};
13400