Sequence example
Input
push(2), push(0), push(3), push(0), get_min(), pop(), get_min()
Output
0 then 0
After pushes the minimum is 0; pop removes the last 0, but a previous 0 remains so min is still 0.
Full lesson preview
Implement a min stack
Build a stack that supports push, pop, top, and retrieving the minimum element in constant time.
Python practice15 minStacks & QueuesIntermediateLast updated March 27, 2026
Problem statement
Design a stack that supports push(x), pop(), top(), and get_min() operations, each in O(1) time. The get_min method should return the minimum element currently in the stack. If an operation that queries the stack (top or get_min) is called when the stack is empty, behavior is undefined (tests will avoid invalid calls). Implement MinStack in Python.
Task
Implement the MinStack class with push(x), pop(), top(), and get_min() methods so that all operations run in O(1) time.
Examples
Input format
Operations will be invoked in test expressions by creating a MinStack instance and calling its methods.
Output format
Values returned by the evaluated expression (typically int).
Constraints
Number of operations in tests is small; expected O(1) per operation; no external libraries.
Samples
Sample 1
Input
(lambda s: (s.push(1), s.push(0), s.get_min())[-1])(MinStack())
Output
0
Push 1 then 0; get_min returns 0.