Question

Formatted question description: https://leetcode.ca/all/345.html

 345	Reverse Vowels of a String

 Write a function that takes a string as input and reverse only the vowels of a string.

 Example 1:

 Input: "hello"
 Output: "holle"

 Example 2:

 Input: "leetcode"
 Output: "leotcede"

 Note:
 The vowels does not include the letter "y".

 @tag-string

Algorithm

It should be noted that capital letters are counted, so there are ten letters in total.

We write a isVowel function to determine whether the current character is a vowel,

If both sides are vowels, then we exchange,
If the one on the left is not, move one place to the right,
If the one on the right is not, move one place to the left

Code

Java

public class Reverse_Vowels_of_a_String {

    class Solution {
        public String reverseVowels(String s) {
            char[] a = s.toCharArray();

            int l = 0; // left
            int r = a.length - 1; // right

            while (l < r) {
                if (isVowel(a[l]) && isVowel(a[r])) {
                    swap(a, l++, r--);
                } else if (isVowel(a[l])) {
                    r--;
                } else {
                    l++;
                }
            }

            return new String(a);
        }

        private boolean isVowel(char b) { // The letters A, E, I, O, and U are called vowels
            char c = Character.toLowerCase(b);
            return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u';
        }

        private void swap(char[] cs, int start, int end) {
            char temp = cs[start];
            cs[start] = cs[end];
            cs[end] = temp;
        }
    }
}

// OJ: https://leetcode.com/problems/reverse-vowels-of-a-string/
// Time: O(N)
// Space: O(1)
class Solution {
private:
    bool isVowel(char c) {
        c = tolower(c);
        return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u';
    }
public:
    string reverseVowels(string s) {
        int i = 0, j = s.size() - 1;
        while (i < j) {
            while (i < j && !isVowel(s[i])) ++i;
            while (i < j && !isVowel(s[j])) --j;
            if (i < j) swap(s[i++], s[j--]);
        }
        return s;
    }
};

class Solution:
    def reverseVowels(self, s: str) -> str:
        vowels = {'a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'}
        i, j = 0, len(s) - 1
        chars = list(s)
        while i < j:
            if chars[i] not in vowels:
                i += 1
                continue
            if chars[j] not in vowels:
                j -= 1
                continue
            chars[i], chars[j] = chars[j], chars[i]
            i += 1
            j -= 1
        return ''.join(chars)

############

import string


class Solution(object):
  def reverseVowels(self, s):
    """
    :type s: str
    :rtype: str
    """
    vowels = set(["a", "e", "i", "o", "u", "A", "E", "I", "O", "U"])
    s = list(s)
    start, end = 0, len(s) - 1
    while start < end:
      if s[start] not in vowels:
        start += 1
      elif s[end] not in vowels:
        end -= 1
      else:
        s[start], s[end] = s[end], s[start]
        start += 1
        end -= 1
    return "".join(s)

345 - Reverse Vowels of a String

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