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 1:

Input: [“H”,”a”,”n”,”n”,”a”,”h”]

Output: [“h”,”a”,”n”,”n”,”a”,”H”]

Solution

from typing import List

class Solution:
    def reverseString(self, s: List[str]) -> None:
        for i in range(int(len(s) / 2)):
            temp = s[i]
            s[i] = s[len(s) - 1 - i]
            s[len(s) - 1 - i] = temp

Test Cases

test = Solution()
testStr = ['a', 'b', 'c']
test.reverseString(testStr)
assert testStr == ['c', 'b', 'a']

testStr = []
test.reverseString(testStr)
assert testStr == []

testStr = ['a']
test.reverseString(testStr)
assert testStr == ['a']
print('All Passed!')

Big O Analysis

Space Complexity: O(1)

Time Complexity: O(N)