In-Place String Reversal

Implement two in-place operations without using additional memory allocation: reverse a string represented as a mutable character array, and swap two integers without using a temporary variable.

Write a function that performs one of the following based on the input mode:

1. mode == "reverse": reverse the list of single-character strings in place.
2. mode == "swap": swap two integers and return the swapped pair.

Formal Specification

• Input:
  • mode, a string equal to "reverse" or "swap"
  • If mode == "reverse", data is a list of single-character strings
  • If mode == "swap", data is a list of exactly two integers
• Output:
  • If mode == "reverse", return the modified character list
  • If mode == "swap", return the swapped two-element list
• Do not use extra arrays, strings, or other auxiliary storage proportional to input size.