FA-96400 / Phone number formatting / Member archive

Variable-length area code grouping: the shortest matching area code is used · case 05

"04012 ..." is grouped as area 040.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Keep digits and drop one leading trunk 0; nine national digits must remain. Numbers starting 7 are mobile with a four-digit block code; otherwise the area code is the longest match from 2, 30, 31, 40, 4012 (no match -> None). The subscriber part is one group if at most 5 digits, two equal halves if even, else 3 then the rest. Return "0" + area + " " + groups joined by spaces.

Why this case matters

Area codes of different lengths share leading digits; choosing the wrong one regroups every digit and prints a number users cannot dial.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
long area code wins over its prefix	`"040 120 5678"`	`"04012 05678"`	Failed

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