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CustomStack Implementation - Step by Step Explanation

In this README, we will walk through the implementation of the CustomStack class in five different programming languages: C++, Java, JavaScript, Python, and Go. The CustomStack class is designed to maintain a stack with additional functionality to increment the bottom k elements. Each section will describe how the core methods (push, pop, and increment) work step by step without revealing the actual code.

C++ Code Explanation

  1. Initialization:

    • The constructor accepts maxSize and initializes two vectors: one for the stack elements and another for tracking increments.

  2. Push Operation:

    • If the current size of the stack is less than maxSize, the new element is added to the stack.
    • Along with the element, an increment placeholder (initialized to 0) is added to a separate vector to track future increments for each stack element.

  3. Pop Operation:

    • If the stack is empty, return -1.
    • The value to be popped is the sum of the top element and any accumulated increments.
    • If the stack has more than one element, the increment of the current element is propagated to the next lower element.
    • Both the element and its corresponding increment placeholder are removed.

  4. Increment Operation:

    • The bottom k elements of the stack are incremented by a given value.
    • This is done by adding the increment to the corresponding position in the inc vector.

Java Code Explanation

  1. Initialization:

    • The constructor accepts maxSize and initializes two lists: one for the stack and another for the increments.

  2. Push Operation:

    • If the stack size is smaller than maxSize, the element is added.
    • A 0 is appended to the inc list, serving as a placeholder for future increments.

  3. Pop Operation:

    • Return -1 if the stack is empty.
    • Otherwise, pop the top element and add any accumulated increment to it.
    • If there are more elements below, propagate the current increment to the element below it.
    • Remove the element and the corresponding increment entry.

  4. Increment Operation:

    • Increment the bottom k elements by a given value.
    • This is done by modifying the inc list at the appropriate position.

JavaScript Code Explanation

  1. Initialization:

    • The constructor takes maxSize and initializes two arrays: one for stack elements and one for increments.

  2. Push Operation:

    • Add an element to the stack if the current size is less than maxSize.
    • Also, append a 0 to the inc array for future increment tracking.

  3. Pop Operation:

    • If the stack is empty, return -1.
    • Otherwise, retrieve the top element and add any pending increment to it.
    • If there are elements below, propagate the current increment to the next lower element.
    • Remove the element and the corresponding increment value.

  4. Increment Operation:

    • Add a value to the bottom k elements by updating the inc array.
    • The increment is applied to the appropriate element in the inc array.

Python Code Explanation

  1. Initialization:

    • The constructor accepts maxSize and initializes two lists: one for the stack and another for the increments.

  2. Push Operation:

    • If the stack has fewer elements than maxSize, push the new element to the stack.
    • Append 0 to the inc list, representing the placeholder for future increments.

  3. Pop Operation:

    • If the stack is empty, return -1.
    • Otherwise, pop the top element and apply any accumulated increment.
    • If there are other elements in the stack, propagate the increment to the next element down.
    • Remove both the top element and its corresponding increment.

  4. Increment Operation:

    • Increment the bottom k elements by updating the value in the inc list.
    • The increment is applied to the lowest k elements via the inc array.

Go Code Explanation

  1. Initialization:

    • The constructor takes maxSize and initializes two slices: one for the stack and another for the increments.

  2. Push Operation:

    • Add the element to the stack if its size is less than maxSize.
    • A zero is appended to the inc slice for future increments.

  3. Pop Operation:

    • If the stack is empty, return -1.
    • Otherwise, the top element is popped and any accumulated increment is applied.
    • If the stack has more than one element, propagate the increment down to the next element.
    • Remove both the element and its increment value.

  4. Increment Operation:

    • Increment the bottom k elements by updating the inc slice.
    • This involves adding the given value to the appropriate position in the inc slice.

Conclusion

In all five implementations, the CustomStack class performs three core operations: push, pop, and increment. While the syntax differs across languages, the underlying logic remains consistent:

  • The push method adds elements up to the maximum size.
  • The pop method removes the top element while applying any pending increments.
  • The increment method allows modifying the bottom k elements efficiently.

Each implementation uses an additional array or list to track the increments, allowing for deferred and efficient handling of bulk updates during the pop operation.