Reverse String

01 · Question

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.

02 · Solution

Reference solution

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)

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