Normalise a phone number
People type phone numbers however they like. The CRM stores exactly one shape, so the importer either produces that shape or rejects the row.
- Throw away everything that is not a digit.
- A single leading zero is a national prefix and is dropped.
- What is left must be exactly ten digits.
- The country code must itself be one to three digits.
- The result is a plus sign, the country code, then the ten digits. Anything that does not fit gives null.
NormalisePhone(raw: string, countryCode: string) → string?
C# needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
public string NormalisePhone(string raw, string countryCode) {
}Worked examples
| Call | Result |
|---|---|
NormalisePhone("0532 123 45 67", "90") | "+905321234567" |
NormalisePhone("532-123-4567", "90") | "+905321234567" |
NormalisePhone("(532) 123 45 67", "1") | "+15321234567" |
NormalisePhone("123", "90") | null |
Hint
Clean, then drop the leading zero, then check the length. Three steps in that order.
Reference solution in C#
public string NormalisePhone(string raw, string countryCode) {
if (countryCode.Length < 1 || countryCode.Length > 3) return null;
foreach (char c in countryCode) if (c < '0' || c > '9') return null;
var d = new StringBuilder();
foreach (char c in raw) if (c >= '0' && c <= '9') d.Append(c);
string s = d.ToString();
if (s.StartsWith("0")) s = s.Substring(1);
return s.Length == 10 ? "+" + countryCode + s : null;
}