345. Reverse Vowels of a String Java Solutions

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

Example 1:
Given s = "hello", return "holle".

Example 2:
Given s = "leetcode", return "leotcede".

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 1 public class Solution {
 2     public String reverseVowels(String s) {
 3         if(null == s) return s;
 4         char[] tmp = s.toCharArray();
 5         Stack<Character> stack = new Stack<Character>();
 6         for(int i = 0; i<tmp.length; i++){
 7             if(isVowels(tmp[i])){
 8                      stack.push(tmp[i]);
 9                 }
10         }
11         for(int i = 0; i<tmp.length; i++){
12             if(isVowels(tmp[i])){
13                     tmp[i] = stack.pop();
14                 }
15         }
16         String res = new String(tmp);
17         return res;
18     }
19     
20     public boolean isVowels(char c){
21         if(c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u' || c == 'A' || c == 'E' || c == 'I' || c == 'O' || c == 'U' ){
22                     return true;
23         }
24         return false;
25     }