Duplicate [mp]

Micro pattern¶

Description¶

Detect, skip, count, or suppress repeated values according to their role in the result.

Problems¶

Check duplicates¶

Use membership, counts, or repeated-state behavior to identify duplicates.

• 217. Contains Duplicate (Top Easy)
• 387. First Unique Character in a String (Top Easy)
• 3. Longest Substring Without Repeating Characters (Top Medium)
• 287. Find the Duplicate Number (Top Hard)

Normalize before deduplication¶

Canonicalize values before inserting them into a uniqueness set.

• 929. Unique Email Addresses (Google Prep)

Skip or count adjacent duplicates¶

Use sorted values or run boundaries to process repeated values together.

• 26. Remove Duplicates from Sorted Array (Top Easy)
• 15. 3Sum (Top Medium)
• 38. Count and Say (Top Medium)

Suppress duplicate search results¶

Deduplicate outputs or remove emitted terminal markers.

• 212. Word Search II (Top Hard)
• 301. Remove Invalid Parentheses (Top Hard)

Deduplicate dependency edges¶

Count a relationship only once when duplicate edges would corrupt a derived degree.

• 1203. Sort Items by Groups Respecting Dependencies (Graph Theory)