Reverse String

LeetCode: https://leetcode.com/problems/reverse-string/

Write a function that reverses a string. The input string is given as an array of characters s. You must do this by modifying the input array in-place with O(1) extra memory.

1def reverseString(s: List[str]) -> None:
2    def helper(l: int, r: int) -> None:
3        if l >= r:
4            return
5        s[l], s[r] = s[r], s[l]
6        helper(l + 1, r - 1)
7    
8    helper(0, len(s) - 1)

Pow(x, n)

Step 1 / 3

Step 1:

Swap the ends (l=0, r=4), then recurse inward.

Pointers: l=0, r=4

Focus: swap @ [0, 4]