Valid Phone Numbers

LeetCode 193 | Difficulty: Easy

Easy

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

Topics: Shell

This problem can typically be solved with straightforward iteration or simple data structure usage. Focus on correctness first, then optimize.

When to use

Basic problems that test fundamental programming skills.

Solution
# Read from the file file.txt and output all valid phone numbers to stdout.
grep -P '^(\d{3}-|\(\d{3}\) )\d{3}-\d{4}$' file.txt

Approach	Time	Space
Solution	$O(n)$	$O(1) to O(n)$

Key Points