- Sorting by wrong endpoint: Merge problems sort by start; scheduling problems often sort by end.
Know which applies.
- Wrong overlap condition: Intervals
[1,3]and[3,5]touching at point may or may not overlap depending on problem definition. - Not handling empty input: Empty interval list should return empty result, not crash.
- Modifying intervals while iterating: Build result in separate list rather than modifying input during processing.