题目描述
题目链接:345. Reverse Vowels of a String
Write a function that takes a string as input and reverse only the vowels of a string.
例子
例子 1
Input: “hello” Output: “holle”
例子 2
Input: “leetcode” Output: “leotcede”
Note
The vowels does not include the letter “y”.
解题思路
通过前后双指针分别向另一侧遍历,每遇到一对元音字符(写一个函数判断字符是否为元音,判断之前先转换大小写)即交换,这里注意遍历过程中一定要保证 前指针 < 后指针
,代码如下:
#include <string>
#include <ctype.h>
class Solution {
public:
std::string reverseVowels(std::string s) {
int front = 0, back = s.length() - 1;
while (front < back && !isVowel(s[front])) front++;
while (front < back && !isVowel(s[back])) back--;
while (front < back) {
std::swap(s[front], s[back]);
front++; back--;
while (front < back && !isVowel(s[front])) front++;
while (front < back && !isVowel(s[back])) back--;
}
return s;
}
private:
bool isVowel(char letter) {
letter = tolower(letter);
return (letter == 'a' || letter == 'e' || letter == 'i' || letter == 'o' || letter == 'u');
}
};
- 时间复杂度: O(n)
- 空间复杂度: O(1)