LeetCode_ String_ Simple_ 344. reverse string

1. subject

Write a function , Its function is to invert the input string . Input string as character array s Given in the form of .
Do not allocate extra space to another array , You have to modify the input array in place 、 Use O(1) To solve this problem .

Example 1：
Input ：s = [“h”,“e”,“l”,“l”,“o”]
Output ：[“o”,“l”,“l”,“e”,“h”]

Example 2：
Input ：s = [“H”,“a”,“n”,“n”,“a”,“h”]
Output ：[“h”,“a”,“n”,“n”,“a”,“H”]

Tips ：
1 <= s.length <= 10⁵
s[i] All are ASCII Printable characters in code table

source ： Power button （LeetCode）
link ：https://leetcode.cn/problems/reverse-string

2. Ideas

（1） Symmetric exchange
Definition i and j, The initial values are 0 and s.length - 1, Then start exchanging s[i] and s[j] Value , Every time I exchange ,i++,j- -, until i >= j End exchange at , At this point, the string is successfully inverted .

3. Code implementation （Java）

// Ideas 1———— Symmetric exchange 
class Solution {
    
    public void reverseString(char[] s) {
    
        int length = s.length;
        for (int i = 0, j = length - 1; i < j; i++, j--) {
    
            char tmp = s[i];
            s[i] = s[j];
            s[j] = tmp;
        }
    }
}