Example 2: What is the output for input ["MinStack","push","push","getMin","pop","getMin"], [[],[1],[0],[],[],[]]?

Output: [null,null,null,0,null,1]. After pushing 1 and 0: getMin returns 0. After popping 0: getMin returns 1.

Min Stack — Stacks Queues Interview Problem

Q: Example 1: What is the output for input ["MinStack","push","push","push","getMin","pop","top","getMin"], [[],[-2],[0],[-3],[],[],[],[]]?

Output: [null,null,null,null,-3,null,0,-2]. After pushing -2, 0, -3: getMin returns -3. After popping -3: top returns 0 and getMin returns -2.

Q: Example 3: What is the output for input ["MinStack","push","push","push","getMin","pop","getMin","pop","getMin"], [[],[2],[1],[3],[],[],[],[],[]]?

Output: [null,null,null,null,1,null,1,null,2]. After pushing 2, 1, 3: getMin returns 1. After popping 3: getMin still returns 1. After popping 1: getMin returns 2.

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.

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

Example 2:

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

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: After pushing -2, 0, -3: getMin returns -3. After popping -3: top returns 0 and getMin returns -2.

Example 2

Input: ["MinStack","push","push","getMin","pop","getMin"], [[],[1],[0],[],[],[]]

Output: [null,null,null,0,null,1]

Explanation: After pushing 1 and 0: getMin returns 0. After popping 0: getMin returns 1.

Example 3

Input: ["MinStack","push","push","push","getMin","pop","getMin","pop","getMin"], [[],[2],[1],[3],[],[],[],[],[]]

Output: [null,null,null,null,1,null,1,null,2]

Explanation: After pushing 2, 1, 3: getMin returns 1. After popping 3: getMin still returns 1. After popping 1: getMin returns 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.

Optimal Complexity

Time

O(1)

Space

O(n)

Examples

Constraints

Optimal Complexity

Choose between solo practice and interview simulation