# !/usr/bin/env python
# -*- coding: utf-8 -*-

'''
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 = 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.

Tags: Stack, Design
'''

class MinStack(object):
    # O(n) runtime, O() space – Minor space optimization
    def __init__(self):
        """
        initialize your data structure here.
        """
        self.stack = []
        self.minstack = []

    def push(self, x):
        """
        :type x: int
        :rtype: void
        """
        self.stack.append(x)
        if not self.minstack:
            self.minstack.append(x)
        elif x <= self.minstack[-1]:
            self.minstack.append(x)

    def pop(self):
        """
        :rtype: void
        """
        if self.stack:
            x = self.stack.pop()
        if x == self.minstack[-1]:
            self.minstack.pop()

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

    def getMin(self):
        """
        :rtype: int
        """
        if self.minstack != []:
            return self.minstack[-1]


class MinStack2(object):
    def __init__(self):
        """
        initialize your data structure here.
        """
        self.stack, self.minstack = [], []

    def push(self, x):
        """
        :type x: int
        :rtype: void
        """
        self.stack.append(x)
        if self.minstack != []:
            if x < self.minstack[-1][0]:
                self.minstack.append([x, 1])
            elif x == self.minstack[-1][0]:
                self.minstack[-1][1] += 1
        else:
            self.minstack.append([x, 1])

    def pop(self):
        """
        :rtype: void
        """
        x = self.stack.pop()
        if x == self.minstack[-1][0]:
            self.minstack[-1][1] -= 1
            if self.minstack[-1][1] == 0:
                self.minstack.pop()

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

    def getMin(self):
        """
        :rtype: int
        """
        if self.minstack != []:
            return self.minstack[-1][0]


# 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()
