Find all indices of a search term in a string

Question

I need a fast method to find all indices of a search term that might occur in a string. I tried this \'brute force\' String extension method:

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Answer 1

Using NSRegularExpression in Swift 4, you can do it like this. NSRegularExpression has been around forever and is probably a better choice than rolling your own algorithm for most cases.

let text = "The quieter you become, the more you can hear."
let searchTerm = "you"

let regex = try! NSRegularExpression(pattern: searchTerm, options: [])
let range: NSRange = NSRange(text.startIndex ..< text.endIndex, in: text)
let matches: [NSTextCheckingResult] = regex.matches(in: text, options: [], range: range)
let ranges: [NSRange] = matches.map { $0.range }
let indices: [Int] = ranges.map { $0.location }
let swiftRanges = ranges.map { Range($0, in: text) }
let swiftIndices: [String.Index] = swiftRanges.flatMap { $0?.lowerBound }