193. Valid Phone Numbers

Problem

Given a text file file.txt that contains a list of phone numbers (one per line), write a one-liner bash script to print all valid phone numbers.

You may assume that a valid phone number must appear in one of the following two formats: (xxx) xxx-xxxx or xxx-xxx-xxxx. (x means a digit)

You may also assume each line in the text file must not contain leading or trailing white spaces.

Example:

Assume that file.txt has the following content:

987-123-4567
123 456 7890
(123) 456-7890

Your script should output the following valid phone numbers:

987-123-4567
(123) 456-7890

Solution

# Read from the file file.txt and output all valid phone numbers to stdout.
egrep '^[0-9]{3}-[0-9]{3}-[0-9]{4}$|^\([0-9]{3}\)\s[0-9]{3}-[0-9]{4}$' file.txt

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).