题目：Reverse String （难度一颗星）
Write a function that takes a string as input and returns the string reversed.
Example:
Given s = "hello", return "olleh".
实现：
1 class Solution {
2 public:
3 string reverseString(string s) {
4 int length = s.length();
5 int start = 0;
6 int ends = length - 1;
7 while(start < ends)
8 {
9 int temp = s[start];
10 s[start] = s[ends];
11 s[ends] = temp;
12 start++;
13 ends--;
14 }
15 return s;
16 }
17 };
题目：Reverse Vowels of a String （难度一颗星）
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".
实现：
1 class Solution {
2 public:
3 bool validate(char c)
4 {
5 return (c == 'a') || (c == 'e') || (c == 'i') || (c == 'o') || (c == 'u') || (c == 'A') || (c == 'E') || (c == 'I') || (c == 'O') || (c == 'U');
6 }
7
8 string reverseVowels(string s) {
9 int starts = 0;
10 int ends = s.size()-1;
11 while (starts < ends)
12 {
13 while (!validate(s[starts]))
14 {
15 starts++;
16 }
17 while (!validate(s[ends]))
18 {
19 ends--;
20 }
21 if (starts > ends)
22 {
23 break;
24 }
25 int temp = s[starts];
26 s[starts] = s[ends];
27 s[ends] = temp;
28 starts++;
29 ends--;
30 }
31 return s;
32 }
33 };