python 18 lines · 6 steps

How interval merging works

Sort intervals by start, then sweep once, extending or appending as overlaps appear.

Explained by highlit
Intermediate sorting greedy intervals single-pass
1from typing import List, Tuple
2 
3 
4def merge_intervals(intervals: List[Tuple[int, int]]) -> List[Tuple[int, int]]:
5 if not intervals:
6 return []
7 
8 ordered = sorted(intervals, key=lambda pair: pair[0])
9 merged = [ordered[0]]
10 
11 for start, end in ordered[1:]:
12 last_start, last_end = merged[-1]
13 if start <= last_end:
14 merged[-1] = (last_start, max(last_end, end))
15 else:
16 merged.append((start, end))
17 
18 return merged
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Sorting by start point guarantees any overlap must involve the most recently kept interval.
  2. 2Extending an interval means taking the max of the two ends, since containment is possible.
  3. 3A single linear sweep after sorting resolves all merges without nested comparisons.

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