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mediumDSA

How do you merge overlapping intervals?

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01

Understand the problem

Explain merge intervals.

intervalssorting
02

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03

Study the solution

Sort intervals by start, then sweep: if the current interval overlaps the last merged one (start <= lastEnd), extend the end; otherwise append it. O(n log n) dominated by the sort.

Solution ready — 2 min read

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04

Read the code

Sort then sweep
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def merge(intervals):
    intervals.sort(key=lambda x: x[0])
    merged = [intervals[0]]
    for start, end in intervals[1:]:
        if start <= merged[-1][1]:           # overlap
            merged[-1][1] = max(merged[-1][1], end)
        else:
            merged.append([start, end])
    return merged


# --- demo ---
print(merge([[1, 3], [2, 6], [8, 10], [15, 18]]))   # [[1, 6], [8, 10], [15, 18]]
05

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