Reverse String

Reverse a string in place — that is the interview version: swap the first and last characters, then the second and second-last, and so on, moving two pointers towards the middle.

Input: one line s (printable characters; it does not start or end with a space).

Output: s reversed.

Constraints: 1 ≤ length of s ≤ 10⁵.

Practise the technique: your language can probably reverse a string in one call — try writing the two-pointer swap loop yourself on an array of characters. That loop is the building block for many harder problems.