Common Mistakes

• 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 $3$ 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.