Problem – Find Overlapping Pipeline Intervals
Find all time intervals during which at least two pipelines are running at the same time.
You are given a list of half-open or closed intervals (assume closed here) where each interval[start, end] represents the running time of one pipeline.
Return all sub-intervals where the number of running pipelines is ≥ 2.
Example
Input:[[2, 5], [12, 15], [4, 8]]
Output:[[4, 5]]
Because between time 4 and 5, both the interval [2, 5] and [4, 8] are running.
In English: Use a sweep-line. Turn each interval into start/end events, sort them, maintain a running count; whenever count goes from 1→2, start an overlap; when it drops from 2→1, close the overlap and record it.
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