2021-10-14 algorithms

# LeetCode's Reverse String: in-place with O(1) extra memory.

Write a function that reverses a string. The input string is given as an array of characters s.

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"]``````

Follow up: Do not allocate extra space for another array. You must do this by modifying the input array in-place with O(1) extra memory.

## My implementation

``````// o - l - l - e - h
// h               a
// h - e -     l   o
// h - e - l - l - o``````

I’ve decided to use the mirroring technique to implement the string reversal algorithm with the objective of obeying the constraint of using O(1) extra memory: No new array shall be created in runtime.

``````/**
* @param {character[]} s
* @return {void} Do not return anything, modify s in-place instead.
*/
var reverseString = function (s) {
let l = 0;
let r = s.length - 1;
while (l < r) {
const tmp = s[l];
s[l] = s[r];
s[r] = tmp;
l++;
r--;
}

return s;
};``````

By using the mirroring technique the following operations are going to be performed on each iteration:

``````What is left will be right.
What is right will be left.``````