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".
Note:
The vowels does not include the letter "y".
**解题思路 **
Two pointers. Use a HashSet<Character> to reduce the look up time to O(1)
public String reverseVowels(String s) {
Set<Character> vowels = new HashSet<>(Arrays.asList(new Character[]{'a','e','i','o','u','A','E','I','O','U'}));
char[] list = s.toCharArray();
for (int i=0, j=list.length-1; i<j; ) {
if (!vowels.contains(list[i])) {
i++;
continue;
}
if (!vowels.contains(list[j])) {
j--;
continue;
}
char temp=list[i];
list[i]=list[j];
list[j]=temp;
i++;
j--;
}
return String.valueOf(list);
}
public String reverseVowels(String s) {
if(s == null || s.length()==0) return s;
String vowels = "aeiouAEIOU";
char[] chars = s.toCharArray();
int start = 0;
int end = s.length()-1;
while(start<end){
while(start<end && !vowels.contains(chars[start]+"")){
start++;
}
while(start<end && !vowels.contains(chars[end]+"")){
end--;
}
char temp = chars[start];
chars[start] = chars[end];
chars[end] = temp;
start++;
end--;
}
return new String(chars);
}
