We use two pointers, left and right, starting at the ends of the array and swap them until they meet in the middle.

1. l = 0, r = len(s) - 1.
2. While l < r:
   • Swap s[l] and s[r].
   • l += 1, r -= 1.

• Time Complexity: O(N).
• Space Complexity: O(1).

def reverse_string(s):
    l, r = 0, len(s) - 1
    while l < r:
        s[l], s[r] = s[r], s[l]
        l += 1
        r -= 1