344 Reverse String

Straight forward algorithm to reverse strings, arrays, lists. Just make sure that you are modifying the memory location, and not just creating a copy.

In Python, s = s[::-1] will not work, because you are not modifying the string slice/in-memory location, you are just modifying the pointer that gives access to that string. Use s[:] = s[::-1] instead.

Code

Python3

def reverseString(self, s: List[str]) -> None:
    """
    Do not return anything, modify s in-place instead.
    """
 
    l, r = 0, len(s)-1
 
    while l < r:
        s[l], s[r] = s[r], s[l]
        l += 1
        r -= 1

Big O Analysis

• Runtime

  The runtime complexity here is $O(N)$ since we would have to traverse the entire string.

• Memory

  The memory usage is $O(1)$ since we do it in-place.

— A

GitHub | Twitter