原题链接在这里：https://leetcode.com/problems/reverse-string/
题目：
Write a function that reverses a string. The input string is given as an array of characters char[].
Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.
You may assume all the characters consist of printable ascii characters.
Example 1:
Input: ["h","e","l","l","o"]
Output: ["o","l","l","e","h"]
Example 2:
Input: ["H","a","n","n","a","h"]
Output: ["h","a","n","n","a","H"]
题解：
Reverse string是常见题, string在Java中是primitive类型, 一旦生成不可改变.
But we have the array of char here. Then use two pointers. Remember to move pointer in while loop.
Time Complexity: O(s.length).
Space: O(1).
AC Java:
1 class Solution { 2 public void reverseString(char[] s) { 3 int l = 0; 4 int r = s.length - 1; 5 6 while(l < r){ 7 char temp = s[l]; 8 s[l] = s[r]; 9 s[r] = temp; 10 11 l++; 12 r--; 13 } 14 } 15 }