Min Stack

Medium~20 min

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

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

Examples

Example 1
Input: ["MinStack","push","push","push","getMin","pop","top","getMin"] [[], [-2], [0], [-3], [], [], [], []]
Output: [null, null, null, null, -3, null, 0, -2]
Explanation: MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); // return -3 minStack.pop(); minStack.top(); // return 0 minStack.getMin(); // return -2

Constraints

  • -2^31 <= val <= 2^31 - 1
  • Methods pop, top and getMin will always be called on non-empty stacks
  • At most 3 * 10^4 calls will be made to push, pop, top, and getMin
  • Expected time complexity: O(1) per operation
Code
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Output

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