How do you solve Valid Phone Numbers on LeetCode?

Valid Phone Numbers (LeetCode #193) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Using regex can simplify the matching process significantly.

What is the time complexity of Valid Phone Numbers?

The optimal solution for Valid Phone Numbers runs in O(n) time and uses O(n) space. This is O(n) because we read the file once and apply regex matching, which is linear with respect to the input size.

What is the brute force solution for Valid Phone Numbers?

The brute force approach for Valid Phone Numbers is Brute Force, with O(n²) time complexity and O(1) space complexity. In this approach, we will check each phone number line by line to see if it matches either of the valid formats. This is straightforward but can be inefficient for large files. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Valid Phone Numbers?

Valid Phone Numbers uses the following concepts: Shell. The recommended patterns to study are: Regular Expressions, String Matching.

What are the interview tips for Valid Phone Numbers?

Always clarify the problem requirements and constraints before coding. Think about edge cases, such as empty lines or unexpected formats. Practice writing regex patterns, as they are often useful in string manipulation problems.

What are common mistakes when solving Valid Phone Numbers?

Not accounting for spaces or incorrect formats in the regex. Overcomplicating the solution with unnecessary loops.

#193

Valid Phone Numbers

Easy

ShellRegular ExpressionsString Matching

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

Using regex patterns allows us to efficiently check for valid phone numbers in a single pass, making this approach much faster and more efficient.

⚙️

Algorithm

3 steps

1Step 1: Read the entire file content at once.
2Step 2: Use a single regex pattern to match both valid formats in one go.
3Step 3: Print all matched phone numbers.

solution.py6 lines

1import re
2with open('file.txt') as f:
3    content = f.read()
4    matches = re.findall(r'\(\d{3}\) \d{3}-\d{4}|\d{3}-\d{3}-\d{4}', content)
5    for match in matches:
6        print(match)

ℹ

Complexity note: This is O(n) because we read the file once and apply regex matching, which is linear with respect to the input size.

1Using regex can simplify the matching process significantly.
2Reading the entire file at once can be more efficient than line-by-line processing.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.