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Grokking the Coding Interview Patterns in Python

Maximum Frequency Stack

Explore how to build a stack-like data structure that prioritizes popping elements with the highest frequency. Understand the use of frequency tracking and tie-breaking by recent insertion, essential for solving complex problems like permutations, anagrams, and game design. This lesson guides you through designing, pushing, and popping operations to efficiently handle frequency-based constraints in coding interviews.

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Statement

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

You’ll need to implement the FreqStack class that should consist of the following:

  • Init(): This is a constructor used to declare a frequency stack.

  • Push(value): This is used to push an integer data onto the top of the stack.

  • Pop(): This is used to remove and return the most frequent element in the stack.

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

Constraints:

  • 0≤0 \leq value ≤104\leq 10^4

  • At most, 2×1032 \times 10^3 calls will be made to Push() and Pop().

  • It is guaranteed that there will be at least one element in the stack before calling Pop().

Examples

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Understand the problem

Let’s take a moment to make sure we have correctly understood the problem. The quiz below helps us to check that we are solving precisely the right problem:

Maximum Frequency Stack

1.

What is the output if four Pop() calls are made onto this stack?

A.

[5, 4, 7, 5]

B.

[5, 7, 4, 5]

C.

[7, 5, 4, 7]

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Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
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Try it yourself

Implement your solution in the following coding playground.

Python
usercode > freq_stack.py
class FreqStack:
    def __init__(self):
        # Write your code here
        pass
    def push(self, value):
        # Write your code here
        pass
    def pop(self):
        # Replace this plaecholder return statement with your code
        return -1
Maximum Frequency Stack