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Maximum Frequency Stack

Understand how to implement a frequency stack that supports pushing elements and popping the most frequent element, resolving ties by most recent insertion. Explore efficient data tracking patterns useful for frequency-related coding interview problems.

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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:

  • FreqStack: This is a class 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.

Java
usercode > FreqStack.java
import java.util.*;
class FreqStack {
    public FreqStack() {
        // Write your code here
    }
    public void push(int value) {
        // Write your code here
    }
    public int pop() {
        // Replace this plaecholder return statement with your code
        return -1;
    }
}
Maximum Frequency Stack