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

"""
Problem Link: https://leetcode.com/problems/design-a-stack-with-increment-operation/

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.
 

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

    def __init__(self, maxSize):
        self.n = maxSize
        self.stack = []
        self.inc = []

    def push(self, x):
        if len(self.inc) < self.n:
            self.stack.append(x)
            self.inc.append(0)

    def pop(self):
        if not self.inc: return -1
        if len(self.inc) > 1:
            self.inc[-2] += self.inc[-1]
        return self.stack.pop() + self.inc.pop()

    def increment(self, k, val):
        if self.inc:
            self.inc[min(k, len(self.inc)) - 1] += 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)