EASY NC#15 Blind #2 Sliding Window
121. Best Time to Buy and Sell Stock
📖 Problem
You are given an array prices where prices[i] is the price of a given stock on the ith day. You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock. Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.
🧠 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
- •String/array indexing
- •Set/Map frequency counting
- •Pointer movement invariants
Logical Thinking Concepts
- •Define invariants before coding
- •Check edge cases first (`[]`, single element, duplicates)
- •Estimate time/space before implementation
- •Apply Sliding Window reasoning pattern
💡 Approach
- → Track minimum price seen so far
- → Calculate profit if sold today (current price - min price)
- → Track maximum profit
- → Time: O(n), Space: O(1)
🛠️ Hints & Pitfalls
Hints
- •Track minimum price seen so far
- •Calculate profit if sold today (current price - min price)
- •Track maximum profit
Common Pitfalls
- •Time: O(n), Space: O(1)
🧪 Test Cases
Hidden tests on submit: 5
Test Case 1
Not run Input:
maxProfit([7, 1, 5, 3, 6, 4]); Expected:
5 Test Case 2
Not run Input:
maxProfit([7, 6, 4, 3, 1]); Expected:
0 Test Case 3
Not run Input:
maxProfit([1]); Expected:
0 📝 Code Editor
📤 Output