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Solution: Number of People Aware of a Secret

Understand how to apply dynamic programming to track the number of people aware of a secret over time, considering delay before sharing and forgetting time. This lesson guides you through building an efficient algorithm to handle day-by-day sharing and forgetting, optimizing with modular arithmetic and incremental updates.

Statement

On day 11, exactly one person discovers a secret.

Each person who learns the secret will begin sharing it with one new person every day, but only after a waiting period of delay days from when they first discovered it. Additionally, each person completely forgets the secret forget days after discovering it. Once a person has forgotten the secret (on the day of forgetting and all subsequent days), they can no longer share it.

Given an integer n, determine how many people know the secret at the end of day n. Since the result can be very large, return it modulo 109+710^9 + 7.

Note: A person who discovered the secret on day d can share it starting from day d + delay through day d + forget - 1 (inclusive), and they forget it on day d + forget.

Constraints:

  • 22 \leq ...