LC155. Min Stack

class MinStack:
 
    def __init__(self):
        self.stack = []
        self.minstack = []
 
    def push(self, val: int) -> None:
        self.stack.append(val)
 
        if len(self.minstack) == 0:
            self.minstack.append(val)
        elif val < self.minstack[-1]:
            self.minstack.append(val)
        else:
            self.minstack.append(self.minstack[-1])
 
    def pop(self) -> None:
        self.stack.pop()
        self.minstack.pop()
 
    def top(self) -> int:
        return self.stack[-1]
 
    def getMin(self) -> int:
        return self.minstack[-1]
 
 
# Your MinStack object will be instantiated and called as such:
# obj = MinStack()
# obj.push(val)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()

Complexity

Time: Push: Amortized $O(1)$, Pop: $O(1)$, Top: $O(1)$, GetMin: $O(1)$
Space: $O(n)$