FA-96729 / Phone number formatting / Member archive

Number list range compression: duplicates split a run · case 04

A repeated number produces a singleton followed by a run.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input a list of digit strings. Deduplicate and sort by (length, text). Consecutive numbers of equal length (each one greater than the previous) form a run. A run of one is emitted as is; a longer run is emitted as START-TAIL where TAIL is END without the prefix it shares with START.

Why this case matters

Number inventories are displayed and exported as compressed ranges; a wrong run boundary or tail misstates which numbers are owned.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
duplicates inside a run	`["5550145", "5550145-6"]`	`["5550145-6"]`	Failed

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