June Leetcoding Challenge(6.4)

Reverse String

1. 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"]

思路：

设置两个指针，一个指针指向首元素l，另一个指针指向末尾元素r，开始进行while循环，循环推出条件为l<r。 通过移动l，r两个指针交换元素。

代码：

class Solution {
    public void reverseString(char[] s) {
        int l = 0;
        int r = s.length-1;
        while(l<r){
            char tmp = s[r];
            s[r] = s[l];
            s[l] =tmp;
            l++;
            r--;
        }
    }
}