# [Leet Code] Design a Stack With Increment Operation

2 min readFeb 6, 2021

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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 = maxSizedef 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)