題目

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"

Note: The vowels does not include the letter “y”.

題目大意

反轉字串中的母音字元

思路

使用雙指標 一個指標從頭向尾遍歷，一個指標從尾到頭遍歷 ，指向待反轉的兩個母音字元。然後交換元素。

class Solution {
    static Set<Character> vowels = new HashSet<>(Arrays.asList('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'));

    public String reverseVowels(String s) {
        int lp = 0,rp = s.length()-1;
        char[] chs = s.toCharArray();
        while(lp<rp){
            while
 
(lp<rp && !vowels.contains(chs[lp]))
                lp++;
            while(lp<rp && !vowels.contains(chs[rp]))
                rp--;
            if(lp<rp){
                char tc = chs[lp];
                chs[lp] = chs[rp];
                chs[rp] = tc;
                lp++
 
;
                rp--;
            }
        }
        return String.valueOf(chs);
    }
}

重新 生成 chars，效能要差些。

class Solution {
    static Set<Character> vowels = new HashSet<>(Arrays.asList('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'));

    public String reverseVowels(String s) {
        int i = 0, j = s.length() - 1;
        char[] result = new char[s.length()];
        while (i <= j) {
            char ci = s.charAt(i);
            char cj = s.charAt(j);
            if (!vowels.contains(ci)) {
                result[i++] = ci;
            } else if (!vowels.contains(cj)) {
                result[j--] = cj;
            } else {
                result[i++] = cj;
                result[j--] = ci;
            }
        }
        return new String(result);
    }
}