new_contents: """Leetcode 155. Min Stack
  Easy
  
  URL: https://leetcode.com/problems/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.
  
  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()
  """
  
  class MinStack(object):
  
      def __init__(self):
          """
          initialize your data structure here.
          """
          pass
  
      def push(self, x):
          """
          :type x: int
          :rtype: None
          """
          pass
  
      def pop(self):
          """
          :rtype: None
          """
          pass
  
      def top(self):
          """
          :rtype: int
          """
          pass
  
      def getMin(self):
          """
          :rtype: int
          """
          pass
  
  
  def main():
      pass
  
  
  if __name__ == '__main__':
      main()
  
subject: Add lc155_min_stack.py