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?
Go 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
func normalisePhone(raw string, countryCode string) *string {
}Worked examples
| Call | Result |
|---|---|
normalisePhone("0532 123 45 67", "90") | pStr("+905321234567") |
normalisePhone("532-123-4567", "90") | pStr("+905321234567") |
normalisePhone("(532) 123 45 67", "1") | pStr("+15321234567") |
normalisePhone("123", "90") | nil |
Hint
Clean, then drop the leading zero, then check the length. Three steps in that order.
Reference solution in Go
func normalisePhone(raw string, countryCode string) *string {
if len(countryCode) < 1 || len(countryCode) > 3 {
return nil
}
for i := 0; i < len(countryCode); i++ {
if countryCode[i] < '0' || countryCode[i] > '9' {
return nil
}
}
d := ""
for i := 0; i < len(raw); i++ {
if raw[i] >= '0' && raw[i] <= '9' {
d += string(raw[i])
}
}
if strings.HasPrefix(d, "0") {
d = d[1:]
}
if len(d) != 10 {
return nil
}
result := "+" + countryCode + d
return &result
}