Day 10: Min Stack.py

# Day 10:  Min Stack
#
# 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 = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin();   --> Returns -3.
minStack.pop();
minStack.top();      --> Returns 0.
minStack.getMin();   --> Returns -2.
"""

class MinStack(object):

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


    def push(self, x):
        """
        :type x: int
        :rtype: None
        """
        self.stack.append(x)
        if len(self.min_stack) == 0 or x <= self.min_stack[-1]:
            self.min_stack.append(x)


    def pop(self):
        """
        :rtype: None
        """
        if self.stack and self.stack.pop() == self.min_stack[-1]:
            self.min_stack.pop()


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


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


# Your MinStack object will be instantiated and called as such:
# obj = MinStack()
# obj.push(x)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()