Min Stack

min_stack.py

"""
Description:
Design a stack that supports push, pop, top, and retrieving the minimum element in
constant time.
- push(x) -- Push element x onto stack.
- pop() -- Removes the element on top of the stack.
- top() -- Get the top element.
- getMin() -- Retrieve the minimum element in the stack.

Example:
minStack = MinStack()
minStack.push(-2)
minStack.push(0)
minStack.push(-3)
minStack.getMin() # -3
minStack.pop()
minStack.top()    # 0
minStack.getMin() # -2
"""

class MinStack:
    def __init__(self):
        """
        initialize your data structure here.
        """
        self.stack = []
        self.mins = []

    def push(self, x):
        """
        :type x: int
        :rtype: void
        """
        self.stack.append(x)
        if len(self.mins) == 0 or self.mins[-1] >= x:
            self.mins.append(x)

    def pop(self):
        """
        :rtype: void
        """
        tmp = self.stack.pop()
        if self.mins[-1] == tmp:
            self.mins.pop()
        return tmp

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

    def getMin(self):
        """
        :rtype: int
        """
        return self.mins[-1]