Merge Intervals — Interview Question Guide

• Sorting by start time turns a pairwise problem into a single linear sweep.
• Two intervals overlap when the next start is ≤ the current end.
• Merge by extending the current end to the max of the two ends.

1. Sort intervals by start time.
2. Initialize the result with the first interval.
3. For each next interval, if it overlaps the last result interval, merge; otherwise append.

def merge(intervals):
    intervals.sort()
    merged = [intervals[0]]
    for s, e in intervals[1:]:
        ls, le = merged[-1]
        if s <= le:
            merged[-1][1] = max(le, e)
        else:
            merged.append([s, e])
    return merged