Leetcode/G家 344.345. Reverse Vowels of a String (2pointer)

345. Reverse Vowels of a String(2pointer)
easy
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:
Given s = "hello", return "holle".

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

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

思路： convert to char array, use two pointer: i - track the vowel from begin; j - track the vowel from end

          once both i & j point to vowel, swap char

public class Solution {
    public String reverseVowels(String s) {
        char[] word = s.toCharArray();
        Set<Character> set = new HashSet<Character>(Arrays.asList('a','e','i','o','u','A','E','I','O','U'));
        int i = 0,j = word.length-1;
        while(i<j){
            char a = word[i];
            char b = word[j];
            if(!set.contains(a)){
                i++;
            }else if(!set.contains(b)){
                j--;
            }else{//a & b both vowel
                word[i] = b;
                word[j] = a;
                i++;
                j--;
            }
        }
        return new String(word);
    }
}

304, simply reverse string

思路： use two pointer i from start, j from end, keep swaping i++, j-- while i < j

public class Solution {
    public String reverseString(String s) {
        char[] word = s.toCharArray();
        int i = 0,j = word.length-1;
        while(i<j){
            char tmp = word[i];
            word[i] = word[j];
            word[j] = tmp;
            i++;
            j--;
        }
        return new String(word);
    }
}