345. Reverse Vowels of a String.md

345. Reverse Vowels of a String (Easy)

[tag] two pointers

• brute force:
  • use for loop to find all vowels and index.
  • reverse them and puth them back to place.
  • hello --> e (1) and o (4) a (5) -> a(1), o(4), e(5)
• two pointers:
  • use l and r pointers move if not vowels
  • if both are vowels, swap them, and both move one more
  • if they meet exist so while condition will be while l < r

class Solution:
    def reverseVowels(self, s: str) -> str:
        if not s:
            return
        s_list = list(s)
        l, r = 0, len(s_list) - 1
        vowels = list('aeiouAEIOU')
        # vowels = ['a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U']
        while l < r:
            while l < r and s_list[l] not in vowels:
                l += 1
            while l < r and s_list[r] not in vowels:
                r -= 1
            s_list[l], s_list[r] = s_list[r], s_list[l]
            l, r = l + 1, r - 1
        return ''.join(s_list)