Reverse String

The most intuitive approach is to build a new reversed array from the original, then copy the values back. This violates the O(1) space requirement.

1. 1Create a copy of the array in reverse order using slicing.
2. 2Copy each element from the reversed copy back into the original array.

Why it's not optimal: Uses O(n) extra space for the copy, violating the in-place constraint.

def reverseString(s):
    rev = s[::-1]
    for i in range(len(s)):
        s[i] = rev[i]

Place one pointer at the start and one at the end. Swap their characters and move both pointers inward until they meet in the middle.

1. 1Initialize L=0 and R=len(s)-1.
2. 2While L < R, swap s[L] and s[R].
3. 3Increment L and decrement R to move inward.
4. 4When pointers meet, the array is fully reversed.