[Leet Code] Design a Stack With Increment Operation

Matthew Boyd
2 min readFeb 6, 2021

Leetcode: https://leetcode.com/problems/design-a-stack-with-increment-operation/

Problem:

Design a stack which supports the following operations.

Implement the CustomStack class:

  • CustomStack(int maxSize) Initializes the object with maxSize which is the maximum number of elements in the stack or do nothing if the stack reached the maxSize.
  • void push(int x) Adds x to the top of the stack if the stack hasn't reached the maxSize.
  • int pop() Pops and returns the top of 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, just 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 customStack = new CustomStack(3); // Stack is Empty []
customStack.push(1); // stack becomes [1]
customStack.push(2); // stack becomes [1, 2]
customStack.pop(); // return 2 --> Return top of the stack 2, stack becomes [1]
customStack.push(2); // stack becomes [1, 2]
customStack.push(3); // stack becomes [1, 2, 3]
customStack.push(4); // stack still [1, 2, 3], Don't add another elements as size is 4
customStack.increment(5, 100); // stack becomes [101, 102, 103]
customStack.increment(2, 100); // stack becomes [201, 202, 103]
customStack.pop(); // return 103 --> Return top of the stack 103, stack becomes [201, 202]
customStack.pop(); // return 202 --> Return top of the stack 102, stack becomes [201]
customStack.pop(); // return 201 --> Return top of the stack 101, stack becomes []
customStack.pop(); // return -1 --> Stack is empty return -1.

Solution:

class CustomStack(object):def __init__(self, maxSize):
"""
:type maxSize: int
"""
self.stack = []
self.maxSize = maxSize
def push(self, x):
"""
:type x: int
:rtype: None
"""
if len(self.stack) < self.maxSize:
self.stack.append(x)
def pop(self):
"""
:rtype: int
"""
if len(self.stack) == 0:
return -1
else:
return self.stack.pop(len(self.stack) - 1)
def increment(self, k, val):
"""
:type k: int
:type val: int
:rtype: None
"""
if k > self.maxSize or k > len(self.stack):
for i in range(len(self.stack)):
self.stack[i] += val
else:
for i in range(k):
self.stack[i] += val
# Your CustomStack object will be instantiated and called as such:
# obj = CustomStack(maxSize)
# obj.push(x)
# param_2 = obj.pop()
# obj.increment(k,val)

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