Intervals

This is a premium interview-preparation course on the **interval** pattern — the family of problems that model each item as a range with a **start** and an **end**, then ask you to merge, count, schedule, or detect overlaps among those ranges. Interviewers love intervals because a single insight unlocks almost the whole category: **sort by start time (or sometimes by end time), then make one left-to-right sweep**. Once the ranges are in order, overlap becomes a local comparison between the current range and the one you are carrying, and greedy choices that look risky turn out to be provably optimal. This course starts with the mechanics — how to represent an interval, when to sort by start versus end, and exactly what overlap means — then works through curated problems grouped by the patterns interviewers actually test: the merge pattern, resource scheduling with a heap, greedy interval selection, and online interval structures such as booking calendars. Every lesson draws the intervals on a number line, dry-runs a concrete input step by step, and shows a clean Java 17 solution.