DIY: Maximum Frequency Stack

Problem statement

Design a stack-like data structure. We should be able to push elements to this data structure and pop elements with maximum frequency.

You have to implement the FreqStack module:

• FreqStack struct declare a frequency stack
• init() constructs an empty frequency stack
• push(obj, data) pushes an integer data onto the top of the stack
• pop(obj) removes and returns the most frequent element in the stack

If there is a tie for the most frequent element, the most recently pushed element is removed and returned.

Note: If the stack is empty, return -1