Leetcode 2327. Number of People Aware of a Secret

Count how many people know a secret after n days when each person starts sharing every day beginning delay days after learning it and stops (forgets) after forget days. This reduces to a DP/sliding-window problem where new sharers on a day equal the sum of people who learned the secret between (day - forget + 1) and (day - delay), with the result modulo 1e9+7.