LeetCode. Min Stack

Problem:

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 1:

-Summary-

Use tuple to save the minimum value and the current value of the stack.

class MinStack:

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

    def push(self, x: int) -> None:
        if not self.stack:
            self.stack.append((x,x))
        else:
            self.stack.append((x,min(x,self.stack[-1][1])))

    def pop(self) -> None:
        if self.stack:
            self.stack.pop()

    def top(self) -> int:
        if self.stack:
            return self.stack[-1][0]
        else:
            return None

    def getMin(self) -> int:
        if self.stack:
            return self.stack[-1][1]
        else:
            return None


# 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()

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