1381-design-a-stack-with-increment-operation.rb

# frozen_string_literal: true

# 1381. Design a Stack With Increment Operation
# Medium
# https://leetcode.com/problems/design-a-stack-with-increment-operation

=begin
Design a stack that supports increment operations on its elements.

Implement the CustomStack class:
* CustomStack(int maxSize) Initializes the object with maxSize which is the maximum number of elements in the stack.
* void push(int x) Adds x to the top of the stack if the stack has not reached the maxSize.
* int pop() Pops and returns the top of the stack or -1 if the stack is empty.
* void inc(int k, int val) Increments the bottom k elements of the stack by val. If there are less than k elements in the stack, increment all the elements in the stack.

Example 1:
Input
["CustomStack","push","push","pop","push","push","push","increment","increment","pop","pop","pop","pop"]
[[3],[1],[2],[],[2],[3],[4],[5,100],[2,100],[],[],[],[]]
Output
[null,null,null,2,null,null,null,null,null,103,202,201,-1]
Explanation
CustomStack stk = new CustomStack(3); // Stack is Empty []
stk.push(1);                          // stack becomes [1]
stk.push(2);                          // stack becomes [1, 2]
stk.pop();                            // return 2 --> Return top of the stack 2, stack becomes [1]
stk.push(2);                          // stack becomes [1, 2]
stk.push(3);                          // stack becomes [1, 2, 3]
stk.push(4);                          // stack still [1, 2, 3], Do not add another elements as size is 4
stk.increment(5, 100);                // stack becomes [101, 102, 103]
stk.increment(2, 100);                // stack becomes [201, 202, 103]
stk.pop();                            // return 103 --> Return top of the stack 103, stack becomes [201, 202]
stk.pop();                            // return 202 --> Return top of the stack 202, stack becomes [201]
stk.pop();                            // return 201 --> Return top of the stack 201, stack becomes []
stk.pop();                            // return -1 --> Stack is empty return -1.

Constraints:
* 1 <= maxSize, x, k <= 1000
* 0 <= val <= 100
* At most 1000 calls will be made to each method of increment, push and pop each separately.
=end

class CustomStack
  def initialize(max_size)
    @stack = []
    @inc = []
    @max_size = max_size
  end

  def push(x)
    return if @stack.size == @max_size
    @stack.push(x)
    @inc.push(0)
  end

  def pop
    return -1 if @stack.empty?
    if @inc.size > 1
      @inc[-2] += @inc.last
    end
    result = @stack.last + @inc.last
    @stack.pop
    @inc.pop
    result
  end

  def increment(k, val)
    k = [k, @stack.size].min
    return if k == 0
    @inc[k - 1] += val
  end
end

# Your CustomStack object will be instantiated and called as such:
# obj = CustomStack.new(max_size)
# obj.push(x)
# param_2 = obj.pop()
# obj.increment(k, val)