_345.java

package com.fishercoder.solutions;

import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

/**
 * 345. 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".*/
public class _345 {
	public static class Solution1 {
		public String reverseVowels(String s) {
			StringBuilder sb = new StringBuilder(s);
			Set<Character> vowels = new HashSet(Arrays.asList('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'));
			//use two pointers approach would be the fastest
			int i = 0;
			int j = s.length() - 1;
			while (i < j) {
				char left = s.charAt(i);
				char right = s.charAt(j);
				while (i < j && !vowels.contains(left)) {
					i++;
					left = s.charAt(i);
				}
				while (i < j && !vowels.contains(right)) {
					j--;
					right = s.charAt(j);
				}
				char temp = left;
				sb.setCharAt(i, right);
				sb.setCharAt(j, temp);
				i++;
				j--;
			}
			return sb.toString();
		}
	}
}