【LeetCode】345. Reverse Vowels of a String

Difficulty: Easy

 More:【目录】LeetCode Java实现

Description

https://leetcode.com/problems/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"

Intuition

Using two pointers.

Solution

    private final static HashSet<Character> vowels = new HashSet<Character>        (
        Arrays.asList('a','e','i','o','u','A','E','I','O','U'));
    public String reverseVowels(String s) {
        if(s==null || s.length()<=0)
            return s;
        int i=0, j=s.length()-1;
        char[] chars = new char[s.length()];
        while(i<=j){
            char ci=s.charAt(i);
            char cj=s.charAt(j);
            if(!vowels.contains(ci))
                chars[i++]=ci;
            else if(!vowels.contains(cj))
                chars[j--]=cj;
            else{
                chars[i++]=cj;
                chars[j--]=ci;
            }
        }
        return String.valueOf(chars);
    }

　　

Complexity

Time complexity : O(n)

Space complexity :  O(1)

What I've learned

1.The use of two pointers.

 More:【目录】LeetCode Java实现