901. Online Stock Span

Online Stock Span (LeetCode 901) is a Medium Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Stack Patterns pattern, in the Monotonic Stack subpattern.

• NeetCode 250 · #54 of 250 · Stack

How to solve Online Stock Span

Online Stock Span is a Monotonic Stack problem, part of Stack Patterns. Master monotonic stack for next greater element, daily temperatures, and stock span problems.

Work towards the solution in these steps:

1. Consider using a stack to keep track of stock prices for efficient retrieval and updates.
2. Think about maintaining a monotonic stack that stores prices in a specific order to help determine spans quickly.
3. When a new price comes in, you might want to pop elements from the stack that are less than or equal to the current price to aggregate their spans.

The reference solution runs in O(1) amortized time and O(N) space.

The Online Stock Span solution and editorial walks through the full approach with reference code.

Problem statement

Design an algorithm that collects daily price quotes for some stock and returns the span of that stock's price for the current day.

The span of the stock's price in one day is the maximum number of consecutive days (starting from that day and going backward) for which the stock price was less than or equal to the price of that day.

- For example, if the prices of the stock in the last four days is [7,2,1,2] and the price of the stock today is 2, then the span of today is 4 because starting from today, the price of the stock was less than or equal 2 for 4 consecutive days.

- Also, if the prices of the stock in the last four days is [7,34,1,2] and the price of the stock today is 8, then the span of today is 3 because starting from today, the price of the stock was less than or equal 8 for 3 consecutive days.

Implement the StockSpanner class:

- StockSpanner() Initializes the object of the class.

- int next(int price) Returns the span of the stock's price given that today's price is price.

Example 1:

Input ["StockSpanner", "next", "next", "next", "next", "next", "next", "next"] [[], [100], [80], [60], [70], [60], [75], [85]] Output [null, 1, 1, 1, 2, 1, 4, 6]

Explanation StockSpanner stockSpanner = new StockSpanner(); stockSpanner.next(100); // return 1 stockSpanner.next(80); // return 1 stockSpanner.next(60); // return 1 stockSpanner.next(70); // return 2 stockSpanner.next(60); // return 1 stockSpanner.next(75); // return 4, because the last 4 prices (including today's price of 75) were less than or equal to today's price. stockSpanner.next(85); // return 6

Constraints:

- 1 <= price <= 105

- At most 104 calls will be made to next.

Topics and companies

Topics: Stack, Design, Monotonic Stack, Data Stream.

Reported in interviews at Amazon.

How to practise Online Stock Span on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(1) amortized time and O(N) space.

Open Online Stock Span in the code editor, or read the Online Stock Span editorial for a worked solution with its approach and complexity analysis.

Where Online Stock Span sits in the DSA pattern sheet

• Stack Patterns pattern guide
• Monotonic Stack subpattern
• The full DSA patterns sheet

Problems related to Online Stock Span

Other problems that use the same Monotonic Stack and Stack Patterns techniques:

• Car Fleet — Medium, same subpattern
• Daily Temperatures — Medium, same subpattern
• Final Prices With a Special Discount in a Shop — Easy, same subpattern
• Find the Most Competitive Subsequence — Medium, same subpattern
• Maximum Width Ramp — Medium, same subpattern
• Next Greater Element I — Easy, same subpattern

Online Stock Span FAQ