leetcode_155_MinStack.py

# Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.
#
# Implement the MinStack class:
#
# MinStack() initializes the stack object.
# void push(int val) pushes the element val onto the stack.
# void pop() removes the element on the top of the stack.
# int top() gets the top element of the stack.
# int getMin() retrieves the minimum element in the stack.

class MinStack:

    def __init__(self):
        self.stack = []
        self.minstack = []

    def push(self, val: int) -> None:
        self.stack.append(val)
        minstackval = val
        if self.minstack:
            minstackval = self.minstack[-1]
        val = min(val, minstackval)
        self.minstack.append(val)

    def pop(self) -> None:
        self.stack.pop()
        self.minstack.pop()

    def top(self) -> int:
        return self.stack[-1]

    def getMin(self) -> int:
        return self.minstack[1]

# Your MinStack object will be instantiated and called as such:

# for each position have minimum
# obj = MinStack()
# obj.push(val)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()