[Leetcode] Problem 1371 - Find the Longest Substring Containing Vowels in Even Counts

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Given the string s, return the size of the longest substring containing each vowel an even number of times. That is, ‘a’, ‘e’, ‘i’, ‘o’, and ‘u’ must appear an even number of times.

Example

No.1

Input: s = “eleetminicoworoep”

Output: 13

Explanation: The longest substring is “leetminicowor” which contains two each of the vowels: e, i and o and zero of the vowels: a and u.

No.2

Input: s = “leetcodeisgreat”

Output: 5

Explanation: The longest substring is “leetc” which contains two e’s.

No.3

Input: s = “bcbcbc”

Output: 6

Explanation: In this case, the given string “bcbcbc” is the longest because all vowels: a, e, i, o and u appear zero times.

Constraints

  • 1 <= s.length <= 5 x 10^5
  • s contains only lowercase English letters.

Code

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public int findTheLongestSubstring(String s) {
    int max = 0;
    char[] vowel = {'a', 'e', 'i', 'o', 'u'};
    int[] index = new int[32];
    Arrays.fill(index, Integer.MIN_VALUE);
    int state = 0;
    index[state] = -1;

    for (int i = 0; i < s.length(); i++) {
        char ch = s.charAt(i);

        for (int j = 0; j < vowel.length; j++) {
            if (ch == vowel[j])
                state ^= 1 << j;
        }

        if (index[state] == Integer.MIN_VALUE)
            index[state] = i;

        // len = j - (i + 1) + 1 = j - i
        max = Math.max(max, i - index[state]);
    }

    return max;
}