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exercism fetch dart phone-number

Phone Number

Clean up user-entered phone numbers so that they can be sent SMS messages.

The North American Numbering Plan (NANP) is a telephone numbering system used by many countries in North America like the United States, Canada or Bermuda. All NANP-countries share the same international country code: 1.

NANP numbers are ten-digit numbers consisting of a three-digit Numbering Plan Area code, commonly known as area code, followed by a seven-digit local number. The first three digits of the local number represent the exchange code, followed by the unique four-digit number which is the subscriber number.

The format is usually represented as

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(NXX)-NXX-XXXX

where N is any digit from 2 through 9 and X is any digit from 0 through 9.

Your task is to clean up differently formatted telephone numbers by removing punctuation and the country code (1) if present.

For example, the inputs

should all produce the output

6139950253

Note: As this exercise only deals with telephone numbers used in NANP-countries, only 1 is considered a valid country code.

Tip

A function with a return type can only return data of that type and null. However the function caller is only expecting one data type.

Example:

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String hello(int a){
    if ( a == 0){
        return "a";
    } else {
        return null;
    }
}

To make it more clear that this function can also return null or more data types, use dynamic.

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dynamic hello(int a){
    if ( a == 0){
        return "a";
    } else {
        return null;
    }
}

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.