<p>Given the string <code>s</code>, return the size of the longest substring containing each vowel an even number of times. That is, &#39;a&#39;, &#39;e&#39;, &#39;i&#39;, &#39;o&#39;, and &#39;u&#39; must appear an even number of times.</p>

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

<pre>
<strong>Input:</strong> s = &quot;eleetminicoworoep&quot;
<strong>Output:</strong> 13
<strong>Explanation: </strong>The longest substring is &quot;leetminicowor&quot; which contains two each of the vowels: <strong>e</strong>, <strong>i</strong> and <strong>o</strong> and zero of the vowels: <strong>a</strong> and <strong>u</strong>.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;leetcodeisgreat&quot;
<strong>Output:</strong> 5
<strong>Explanation:</strong> The longest substring is &quot;leetc&quot; which contains two e&#39;s.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;bcbcbc&quot;
<strong>Output:</strong> 6
<strong>Explanation:</strong> In this case, the given string &quot;bcbcbc&quot; is the longest because all vowels: <strong>a</strong>, <strong>e</strong>, <strong>i</strong>, <strong>o</strong> and <strong>u</strong> appear zero times.
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 5 x 10^5</code></li>
	<li><code>s</code>&nbsp;contains only lowercase English letters.</li>
</ul>

// // class Solution {
// //   public:
// //     int findTheLongestSubstring(string s) {
// //         int bitMask = 0;
// //         unordered_map<int, int> memo;
// //         unordered_set<char> set{'a', 'e', 'i', 'o', 'u'};
// //         memo.insert({bitMask, -1});
// //         int ret = 0;
// //         for (int i = 0; i < s.size(); ++i) {
// //             if (set.count(s[i])) {
// //                 bitMask ^= (1 << (s[i] - 'a'));
// //             }
// //             if (memo.count(bitMask)) {
// //                 ret = max(ret, i - memo[bitMask]);
// //             } else {
// //                 memo.insert({bitMask, i});
// //             }
// //         }
// //         return ret;
// //     }
// // };

class Solution {
public:
    int findTheLongestSubstring(string s) {
        int bitMask = 0;
        int memo[32]; // 取代 unordered_map，用于记录 bitMask 对应的最早出现的位置
        fill(begin(memo), end(memo), -2); // 初始化数组元素为 -2
        memo[0] = -1; // bitMask 为 0 时，初始位置为 -1
        int ret = 0;
        
        for (int i = 0; i < s.size(); ++i) {
            // 通过数组查找元音字符
            if (s[i] == 'a') bitMask ^= (1);
            else if (s[i] == 'e') bitMask ^= (2);
            else if (s[i] == 'i') bitMask ^= (4);
            else if (s[i] == 'o') bitMask ^= (8);
            else if (s[i] == 'u') bitMask ^= (16);

            // 判断当前 bitMask 是否已经出现过
            if (memo[bitMask] != -2) {
                ret = max(ret, i - memo[bitMask]);
            } else {
                memo[bitMask] = i;
            }
        }
        return ret;
    }
};








auto init = []() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    return 'c';
}();



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