Reverse Vowel

Given a string s, reverse only all the vowels in the string and return it. The vowels are 'a', 'e', 'i', 'o', and 'u', and they can appear in both cases.

Source

package questions

import _utils.UseCommentAsDocumentation
import utils.shouldBe

/**
 * Given a string s, reverse only all the vowels in the string and return it.
 * The vowels are 'a', 'e', 'i', 'o', and 'u', and they can appear in both cases.
 *
 * [Source](https://leetcode.com/problems/reverse-vowels-of-a-string/)
 */
@UseCommentAsDocumentation
private fun reverseVowels(s: String): String {
    if (s.length == 1) {
        return s
    }
    val arr = s.toCharArray()
    var front = 0
    var back = s.lastIndex

    while (true) {
        while (front <= arr.lastIndex && !isVowel(arr[front])) {
            front++
        }
        while (back >= 0 && !isVowel(arr[back])) {
            if (back < 0) break
            back--
        }
        if (front >= back) {
            break
        }
        swap(arr, front, back)
        front++
        back--
    }
    return arr.joinToString("")
}

private fun swap(arr: CharArray, i1: Int, i2: Int) {
    val temp: Char = arr[i1]
    arr[i1] = arr[i2]
    arr[i2] = temp
}

private fun isVowel(char: Char): Boolean {
    return char == 'a' || char == 'e' || char == 'i' || char == 'o' || char == 'u' || char == 'A' || char == 'E' || char == 'I' || char == 'O' || char == 'U'
}

fun main() {
    reverseVowels(s = "hello") shouldBe "holle"
    reverseVowels(s = "leetcode") shouldBe "leotcede"
    reverseVowels(s = ",.") shouldBe ",."
}

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Updated on 2021-10-15