[FEATURE REQUEST] Add Stock Span Problem algorithm in Java

[oleksii-tumanov]

What would you like to Propose?

I want to add an implementation of the Stock Span Problem to the Java repository.

The Stock Span Problem is a classic monotonic-stack algorithm that computes, for each day, how many consecutive previous days had a stock price less than or equal to the current day's price. The implementation runs in linear time using a stack of indices.

Issue details

Expected behavior:
Given an array of stock prices, the algorithm should return an array where each position contains the span for that day.

Example:

• prices: [100, 80, 60, 70, 60, 75, 85]
• expected result: [1, 1, 1, 2, 1, 4, 6]

Planned/implemented test coverage:

• mixed example arrays
• increasing prices
• decreasing prices
• repeated equal prices
• empty array
• single-element array
• null input throws IllegalArgumentException

Additional Information

No response