Merge overlapping intervals in a collection of ranges

How to frame this at Monzo: Connect your answer to measurable impact, clarity of thought, and trade-offs the team cares about. Below is a strong baseline response you can adapt with your own project examples.

Sort intervals by start time. Iterate: if current interval overlaps last merged (start ≤ last end), extend last end; else append new interval.

function merge(intervals) {
  if (!intervals.length) return [];
  intervals.sort((a, b) => a[0] - b[0]);
  const out = [intervals[0]];
  for (let i = 1; i < intervals.length; i++) {
    const [s, e] = intervals[i];
    const last = out[out.length - 1];
    if (s <= last[1]) last[1] = Math.max(last[1], e);
    else out.push([s, e]);
  }
  return out;
}

Time O(n log n) for sort, O(n) scan. Space O(n) for output.

Follow-ups: insert interval into sorted list, meeting rooms minimum count (min-heap on end times), and interval intersection of two lists.