Solved: regular expression for number less than 100

Regular expressions, commonly referred to as regex, are a powerful tool used for pattern matching and manipulation in strings. In the world of programming, they can be quite beneficial, particularly when dealing with massive amounts of data. In this article, we will delve deep into crafting a regex for a number less than 100 using Swift – Apple’s robust and intuitive programming language.

Let’s start with the solution.

import Foundation

let pattern = "^[1-9][0-9]?$|^100$"
let regex = try NSRegularExpression(pattern: pattern)

func matches(_ input: String) -> Bool {
    let range = NSRange(location: 0, length: input.utf16.count)
    return regex.firstMatch(in: input, options: [], range: range) != nil

The implementation above, while seemingly straightforward, requires a comprehensive understanding of both Swift and Regex. Let’s break it down step-by-step.

The first line of code is an import statement. Here, Foundation, one of Apple’s many comprehensive libraries, is imported. Foundation provides a wide range of capabilities, including string handling and pattern matching.

Following the import statement, we define our Regular Expression pattern. This pattern matches any one or two-digit numbers, as well as the number 100. The “^[1-9][0-9]?$” part matches any two-digit number from 10 to 99, and “^100$” matches the number 100.

Next, we create an instance of NSRegularExpression. This is a powerful class available in Foundation that provides rich, flexible, and Unicode-compliant Regex capability to Swift.

NSRegularExpression and Its Role

  • The NSRegularExpression class is a Swift library used to represent and apply regular expressions. It encapsulates the pattern and provides methods to match the regular expression against given strings.
  • NSRegularExpression comes with different options which affect the matching process. However, in our case, we’re using the default options.

Finally, we define a helper function, “matches”, which returns true if the input string matches the regular expression and false otherwise.

Understanding Regular Expressions in Swift

Understanding what regular expressions are and how to utilize them can significantly impact your Swift programming efficiency. A regular expression defines a search pattern for strings and can be used to check if a string contains the specified search pattern.

This code specifies the regular expression pattern for numbers less than 100. It is then wrapped with NSRegularExpression class, offering methods and properties to work with regular expressions effectively.

The NSTextCheckingResult is used to describe the result of a match in NSRegularExpression. In this scenario, we use the firstMatch method to find whether or not the range of the first match of the regular expression in the specified string is nil. If it’s not nil, the string fits our regex pattern; hence the function returns true. Otherwise, if there is no match found (i.e. firstMatch returns nil), the function returns false.

Regular Expressions are incredibly powerful and can be crafted to fit a wide array of pattern matching needs. Having this tool in your programming arsenal will greatly improve the efficiency of your data parsing and string manipulation jobs. Apply Swift’s NSRegularExpression class today to handle your Regex needs effectively.

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