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

Instead of checking for the search term at each position of the string you could use rangeOfString() to find the next occurrence (hoping that rangeOfString() uses more advanced algorithms):

extension String {

    func indicesOf(searchTerm:String) -> [Int] {
        var indices = [Int]()
        var pos = self.startIndex
        while let range = self.rangeOfString(searchTerm, range: pos ..< self.endIndex) {
            indices.append(distance(self.startIndex, range.startIndex))
            pos = range.startIndex.successor()
        }
        return indices
    }
}

Generally, it depends on the size of the input string and the size of the search string which algorithm is "the fastest". You'll find an overview with links to various algorithms in String searching algorithm.

Update for Swift 3:

extension String {

    func indices(of searchTerm:String) -> [Int] {
        var indices = [Int]()
        var pos = self.startIndex
        while let range = range(of: searchTerm, range: pos ..< self.endIndex) {
            indices.append(distance(from: startIndex, to: range.lowerBound))
            pos = index(after: range.lowerBound)
        }
        return indices
    }
}