1、题目
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".
2、思路
根据题意可知，需要将string反转，java中的String是不可变对象，首先想到将String转成StringBuilder，然后定义两个指针i、j，分别指向stringBuilder的首尾位置，分别移动i和j，当i、j同时指向元音字母时，交换所指位置的值。
3、实现(Java)
public String reverseVowels2(String s) {
int i = 0;
int j = s.length() - 1;
StringBuffer sb = new StringBuffer(s);
HashSet vowelSet = new HashSet();
vowelSet.add('a');
vowelSet.add('e');
vowelSet.add('i');
vowelSet.add('o');
vowelSet.add('u');
vowelSet.add('A');
vowelSet.add('E');
vowelSet.add('I');
vowelSet.add('O');
vowelSet.add('U');
while (i < j)
{
if (!vowelSet.contains(ch[i]))
{
i++;
continue;
}
if (!vowelSet.contains(ch[j]))
{
j--;
continue;
}
char c = sb.charAt(i);
sb.setCharAt(i, sb.charAt(j));
sb.setCharAt(j, c);
i++;
j--;
}
return sb.toString();
}
发现这样做耗时较长为10ms,于是直接使用String的
toCharArray()方法将字符串转为字符数组。发现耗时减少为6ms,使用一个条件判断将HashSet替换掉。
4、修改后(Java)
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';
}
public String reverseVowels2(String s) {
int i = 0;
int j = s.length() - 1;
char[] ch = s.toCharArray();
while (i < j)
{
if (!isVowel(ch[i]))
{
i++;
continue;
}
if (!isVowel(ch[j]))
{
j--;
continue;
}
char c = ch[i];
ch[i] = ch[j];
ch[j] = c;
i++;
j--;
}
return String.valueOf(ch);
}
