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Min Stack

medium

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

Implement the MinStack class:

  • MinStack() initializes the stack object.
  • void push(int val) pushes the element val onto the stack.
  • void pop() removes the element on the top of the stack.
  • int top() gets the top element of the stack.
  • int getMin() retrieves the minimum element in the stack.

You must implement a solution with O(1) time complexity for each function.

Test Cases

Copy an input into the main harness and Run to verify
Input
push(-2), push(0), push(-3), getMin(), pop(), top(), getMin()
Expected Output
-3, 0, -2

Explanation: After pushing -2, 0, -3 the min is -3. Popping leaves 0 on top and min becomes -2.

Constraints

  • -2^31 <= val <= 2^31 - 1
  • Methods pop, top and getMin operations will always be called on non-empty stacks.
  • At most 3 * 10^4 calls will be made to push, pop, top, and getMin.

Hints

Hint 1 — click to reveal

A second stack can track the current minimum at each depth.

Hint 2 — click to reveal

Push to the min-stack only when the new value is <= the current min.

Java Compiler

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