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Valid Phone Numbers

Difficulty: Easy

Problem Description

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. A valid phone number must appear in one of the following two formats: (xxx) xxx-xxxx or xxx-xxx-xxxx. Each line in the text file must not contain leading or trailing white spaces.

Key Insights

  • Valid phone numbers can be in two specific formats.
  • The task involves pattern matching to filter valid numbers.
  • Shell scripting provides tools for text processing and pattern matching.

Space and Time Complexity

Time Complexity: O(n), where n is the number of lines in the file. Space Complexity: O(1), as we only store the valid lines temporarily.

Solution

The solution involves using a combination of grep and regex to filter valid phone numbers from the input file. The approach leverages pattern matching to identify lines that conform to the specified phone number formats. The regex patterns will target the specific structure of valid phone numbers.

Code Solutions

# This problem is solved using a bash one-liner, but for educational purposes, 
# a Python equivalent could be shown as follows.
import re

# Read the file and filter valid phone numbers
with open('file.txt') as f:
    valid_numbers = [line.strip() for line in f if re.match(r'^\(\d{3}\) \d{3}-\d{4}$|^\d{3}-\d{3}-\d{4}$', line)]
    for number in valid_numbers:
        print(number)
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