YYYY-MM-DD — Challenge title

Difficulty: 🟢 Easy / 🟡 Medium / 🔴 Hard Pattern: the pattern that solves it Time-box: 20 minutes

Problem

State the problem precisely. Say what to return.

input   -> output      # brief note on why

Hint (open only if stuck after 10 minutes)

Point at the insight without giving the code. Name the pattern, or ask the question that unlocks it.

Solution

def solve(...):
    ...

How it works. Explain the idea, not line by line.

Complexity. Time: O(?) — why. Space: O(?) — why.

Edge cases that matter. Empty input, single element, all-equal values, negatives, the case that breaks the naive approach.

Common wrong answer. The plausible-looking approach that fails, and the input that exposes it.