#Coding 2

Implement a function to reverse a linked list in groups of size k. For example, given the linked list A → B → C → D → E and k = 2, the output should be B → A → D → C → E. If the remaining nodes are less than k, they should remain unchanged.

Solve a medium-level tree traversal problem.

Solve a variation of the Longest Repeating Character Replacement problem.