Is Valid Phone Numbers easy or hard?

The problem is classified as Easy because it focuses on correct pattern matching rather than algorithmic complexity. Understanding regex anchors, digit groups, and exact formatting is the main challenge.

Valid Phone Numbers Python/Java solution

In Python or Java, read each line and apply a compiled regex pattern like ^([0-9]{3}-[0-9]{3}-[0-9]{4}|$[0-9]{3}$ [0-9]{3}-[0-9]{4})$. If the line matches, print or store it. This approach maintains O(n) time complexity with constant extra memory.

How to solve Valid Phone Numbers in O(n)?

Read the file line by line and validate each line using a regex pattern that matches the two allowed formats. Anchors (^ and $) ensure the entire line follows the structure. Tools like grep or awk apply the pattern to every line, producing an O(n) scan of the file.

What is the best approach for Valid Phone Numbers?

Regular expression matching using shell utilities like grep is the most efficient and concise approach. A single regex can enforce both valid formats: xxx-xxx-xxxx and (xxx) xxx-xxxx. The solution scans each line once, resulting in O(n) time complexity with constant extra space.

Is Valid Phone Numbers asked at Google/Amazon/Meta?

The problem focuses on regex and shell command skills rather than complex algorithms. Variants of pattern validation and text filtering appear in system scripting interviews and DevOps-style assessments at large companies, including teams within Google and Amazon that evaluate command-line proficiency.

What data structure is used in Valid Phone Numbers?

No complex data structure is required. The problem relies on pattern matching and sequential file processing. Implementations typically use regular expressions or simple string checks while reading lines from the file.

What is the time complexity of Valid Phone Numbers?

The time complexity is O(n), where n is the number of lines in the input file. Each line is checked once against a regex pattern or a set of character validation rules. Space complexity remains O(1) because the solution processes lines sequentially without storing additional data structures.

Description Solution Video 6:22

193. Valid Phone Numbers

Easy26.6% acceptance4 companies

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

Asked at 4 companies

Microsoft

Google Amazon Meta

Topics

Shell

6:22

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