Question:

Write a function that takes a string as input and reverse only the vowels of a string.

Example 1:

示例Input: "hello"
Output: "holle"

Example 2:

示例Input: "leetcode"
Output: "leotcede"

Solution:

我们只能交换元音字母。此题和将奇数放后面偶数放前面类似。

JAVAclass Solution {
    public String reverseVowels(String s) {
        char[] a = s.toCharArray();
        int i=0;int j=a.length-1;
        while(i < j) {
            while(i < j && !isVowel(a[i])) {
                i++;
            }
            while(j >= 0 && !isVowel(a[j])) {
                j--;
            }
            if (i < j) {
                char t = a[i];
                a[i] = a[j];
                a[j] = t;
                i++;j--;
             }
        }
        return new String(a);
    }
    private boolean isVowel(char c) {
        return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u' ||
            c == 'A' || c == 'E' || c == 'I' || c == 'O' || c == 'U';
    }
}