Number Padding Utility

A Rust utility that pads numbers in strings with leading zeros.

Overview

This utility takes an input string and a padding length, then returns a new string where all numbers in the original string are left-padded with zeros to reach the specified length. Numbers that are already at or above the specified length remain unchanged.

Features

• Pads all whole numbers found in an input string with leading zeros
• Handles strings with multiple numbers
• Preserves non-numeric parts of the string
• Efficiently processes text using regular expressions
• Comprehensive test suite

Implementation Details

This utility uses Rust's regex crate to efficiently identify and process numbers within text:

• Pattern \d+ matches one or more consecutive digits
• replace_all function applies padding to each match
• Zero-padding is implemented with Rust's format specifier {:0>width$}

Examples

pad_numbers("James Bond 7", 3)       -> "James Bond 007"
pad_numbers("PI=3.14", 2)            -> "PI=03.14"
pad_numbers("It's 3:13pm", 2)        -> "It's 03:13pm"
pad_numbers("It's 12:13pm", 2)       -> "It's 12:13pm" (no padding needed)
pad_numbers("99UR1337", 6)           -> "000099UR001337"

Complexity Analysis

Time Complexity

• O(n) where n is the length of the input string
  • The regex engine scans the entire input string once to find all digit sequences
  • Each matched number is processed in constant time for the padding operation
  • The overall time complexity is dominated by the linear scan of the input string

Space Complexity

• O(n) where n is the length of the input string
  • In the worst case (all characters are digits that need padding), the resulting string could be substantially larger than the input
  • The space required is proportional to the length of the input string plus any additional characters added through padding
  • The regex engine itself requires a small constant amount of additional memory

Installation

Add this to your Cargo.toml:

[dependencies]
spark-coding-challenge1 = { git = "https://github.com/yourusername/spark-coding-challenge1" }

Build and Test

# Build the project
cargo build

# Run the tests
cargo test

# Run with additional verbosity
cargo test --verbose

License

MIT