LeetCode 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".

题意：翻转给定字符串中的元音字母。英语中的元音字母有五个：a, e, i, o, u. 字母y是半元音，题中已经申明元音字母不包括y.

思路：用两个标志位left和right，分别从数组的两端开始判断当前字母是否为元音，如果两边字母同时都是元音字母，则交换；如果左边字母不是元音，则左边标志位left加1；如果右边字母不是元音，则右边标志位right加1。另：要考虑字母的大小写

解法一：用String类的contains(CharSequence s)方法，代码如下：

public String reverseVowels(String s){
        if(s == null || s.length() == 0)
            return s;
        char[] chars = s.toCharArray();
        int left = 0, right = chars.length - 1;
        String str = "aeiou";
        char ch;
        boolean lFlag, rFlag;
        while(left < right){
            lFlag = str.contains(String.valueOf(chars[left]).toLowerCase());
            rFlag = str.contains(String.valueOf(chars[right]).toLowerCase());
            if(!lFlag)
                left++;
            else if(!rFlag)
                right--;
            else if(lFlag && rFlag){
                ch = chars[right];
                chars[right] = chars[left];
                chars[left] = ch;
                left++;
                right--;
            }
        }
        return String.valueOf(chars);
    }

解法二：利用自定义的函数判断字母是否为元音

点评：运行时间比上一个方法更短

public String reverseVowels(String s){
        if(s == null || s.length() == 0)
            return s;
        char[] chars = s.toCharArray();
        int left = 0, right = chars.length - 1;
        char ch;
        boolean lFlag, rFlag;
        while(left < right){
            lFlag = isVowels(Character.toLowerCase(chars[left]));
            rFlag = isVowels(Character.toLowerCase(chars[right]));
            if(!lFlag)
                left++;
            else if(!rFlag)
                right--;
            else if(lFlag && rFlag){
                ch = chars[right];
                chars[right] = chars[left];
                chars[left] = ch;
                left++;
                right--;
            }
        }
        return String.valueOf(chars);
    }
    public boolean isVowels(char ch){
        if(ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u')
            return true;
        else 
            return false;
    }