LeetCode 345. Reverse Vowels of a String（翻转元音字母）

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原题网址：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".

方法：使用两个指针。

public class Solution {    boolean[] vowel = { true, false, false, false, true, false, false, false, true, false, false, false, false, false,        true, false, false, false, false, false, true, false, false, false, false, false };    public String reverseVowels(String s) {        if (s == null) return null;        char[] sa = s.toCharArray();        int i=0, j=sa.length-1;        while (i<j) {            while (i<j && (!Character.isLetter(sa[i]) || (Character.isLowerCase(sa[i]) && !vowel[sa[i]-'a']) || (Character.isUpperCase(sa[i]) && !vowel[sa[i]-'A']))) i++;            while (i<j && (!Character.isLetter(sa[j]) || (Character.isLowerCase(sa[j]) && !vowel[sa[j]-'a']) || (Character.isUpperCase(sa[j]) && !vowel[sa[j]-'A']))) j--;            if (i>=j) break;            char c = sa[i];            sa[i] = sa[j];            sa[j] = c;            i++;            j--;        }        return new String(sa);    }}

另一种实现：

public class Solution {    public String reverseVowels(String s) {        char[] sa = s.toCharArray();        int left = 0, right = sa.length-1;        while (left < right) {            while (left < right && !vowel(sa[left])) left ++;            while (left < right && !vowel(sa[right])) right --;            if (left < right) {                char ch = sa[left];                sa[left] = sa[right];                sa[right] = ch;                left ++;                right --;            }        }        return new String(sa);    }    private boolean vowel(char ch) {        if (ch >= 'a') ch -= 'a'-'A';        return ch == 'A' || ch == 'E' || ch == 'I' || ch == 'O' || ch == 'U';    }}

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