Solution.py

"""
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:

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

    def push(self, x: int) -> None:
        self.stk.append(x)
        if not self.mins:
            self.mins.append(x)
            return
        if x <= self.mins[-1]:
            self.mins.append(x)

    def pop(self) -> None:
        val = self.stk.pop()
        if val == self.mins[-1]:
            self.mins.pop()
        

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

    def getMin(self) -> int:
        return self.mins[-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()