reverse_vowels_of_a_string.go

package main

import "unicode"

// Time Complexity: O(N)
// Space Complexity: O(N)

// fun fact:
// `Y` and `y` can be a vowel as well sometimes.
// glad the problem statement defines it well
func isVowel(c rune) bool {
	// alternatively, we can just check
	// return c == 'A' || c == 'E' || c == 'I' || c == 'O' || c == 'U' ||
	//        c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u'
	c = unicode.ToLower(c)
	return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u'
}

func reverseVowels(s string) string {
	ss := []rune(s)
	n := len(ss)
	l, r := 0, n-1
	for l < r {
		// find the index of the first vowel in the given range
		for l < r && !isVowel(ss[l]) {
			l += 1
		}
		// find the index of last vowel in the given range
		for r > l && !isVowel(ss[r]) {
			r -= 1
		}
		// swap ss[l] and ss[r]
		ss[l], ss[r] = ss[r], ss[l]
		// since we've processed the character ss[l],
		// we move the left pointer to the right
		l += 1
		// since we've processed the character ss[r],
		// we move the right pointer to the left
		r -= 1
	}
	return string(ss)
}