MEDIUM NC#22 Stack
155. Min Stack
📖 Problem
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.
🧠 Visual Learning Aid
1 Model the input into the right structure
2 Choose the core technique and invariant
3 Execute step-by-step with a sample
4 Validate complexity and edge cases
JS/TS Refreshers
- •Array methods (`push`, `pop`, `shift`, `slice`)
- •Object/Map/Set usage patterns
- •Function parameter and return typing
Logical Thinking Concepts
- •Define invariants before coding
- •Check edge cases first (`[]`, single element, duplicates)
- •Estimate time/space before implementation
💡 Approach
- → Use auxiliary stack to track minimums
- → When pushing, push to minStack if <= current min
- → When popping, pop from minStack if removing the min
- → Time: O(1) for all operations, Space: O(n)
🧭 Prerequisites
🛠️ Hints & Pitfalls
Hints
- •Use auxiliary stack to track minimums
- •When pushing, push to minStack if <= current min
- •When popping, pop from minStack if removing the min
Common Pitfalls
- •Time: O(1) for all operations, Space: O(n)
🧪 Test Cases
Hidden tests on submit: 5
Test Case 1
Not run Input:
(() => { const minStack = new MinStack(); return minStack.push(-2); })(); Expected:
null Test Case 2
Not run Input:
(() => { const minStack = new MinStack(); minStack.push(-2); return minStack.push(0); })(); Expected:
null Test Case 3
Not run Input:
(() => { const minStack = new MinStack(); minStack.push(-2); minStack.push(0); return minStack.push(-3); })(); Expected:
null 📝 Code Editor
📤 Output