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Question

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

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 lower and upper cases, more than once.

 

Example 1:

Input: s = "hello"
Output: "holle"

Example 2:

Input: s = "leetcode"
Output: "leotcede"

 

Constraints:

• 1 <= s.length <= 3 * 105
• s consist of printable ASCII characters.

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
• C++
• Python
• Go

• 
  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;
          }
      }
  }
  
  ############
  
  class Solution {
      public String reverseVowels(String s) {
          Set<Character> vowels
              = new HashSet<>(Arrays.asList('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'));
          int i = 0, j = s.length() - 1;
          char[] chars = s.toCharArray();
          while (i < j) {
              if (!vowels.contains(chars[i])) {
                  ++i;
                  continue;
              }
              if (!vowels.contains(chars[j])) {
                  --j;
                  continue;
              }
              char t = chars[i];
              chars[i] = chars[j];
              chars[j] = t;
              ++i;
              --j;
          }
          return new String(chars);
      }
  }
  

• // 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
              elif chars[j] not in vowels:
                  j -= 1
              else:
                  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)
  
  

• func reverseVowels(s string) string {
  	left, right := 0, len(s)-1
  	a := []byte(s)
  	for left < right {
  		for left < right && !isVowel(a[left]) {
  			left++
  		}
  		for left < right && !isVowel(a[right]) {
  			right--
  		}
  		if left != right && isVowel(a[left]) && isVowel(a[right]) {
  			a[left], a[right] = a[right], a[left]
  			left++
  			right--
  		}
  	}
  	return string(a)
  }
  
  func isVowel(b byte) bool {
  	return b == 'a' || b == 'e' || b == 'i' || b == 'o' || b == 'u' ||
  		b == 'A' || b == 'E' || b == 'I' || b == 'O' || b == 'U'
  }
  
  

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