A_wrong_KMP_implementation.swift

let string = "XCVBNMDFGHJRTYUERTYUSDFZDFWEDFASDASWE"
string.characters.count

let targetString = "ASWE"
targetString.characters.count

private class Substring {
    var range: Range<String.Index>
    var content: String
    
    var matched: Bool?
    
    init(content: String, range: Range<String.Index>) {
        self.content = content
        self.range = range
    }
}

func findString(targetString: String, inString containerString: String) -> [Range<String.Index>] {
    
    var substrings = [Substring]()
    
    let targetCount = targetString.characters.count
    let characterCount = containerString.characters.count
    
    guard targetCount > 0 && targetCount <= characterCount else {
        return []
    }
    
    for (index, eachContained) in containerString.characters.enumerate() {
        let characterIndex = advance(string.startIndex, index)
        
        for eachSubstring in substrings
            where eachSubstring.matched == nil
        {
            let indexInTargetString = advance(targetString.startIndex, eachSubstring.content.characters.count)
            
            if indexInTargetString < targetString.endIndex {
                let characterInTargetString = targetString[indexInTargetString]
                if eachContained == characterInTargetString {
                    eachSubstring.content.append(eachContained)
                    eachSubstring.range.endIndex = eachSubstring.range.endIndex.successor()
                    
                    if eachSubstring.content.endIndex == targetString.endIndex {
                        eachSubstring.matched = true
                    }
                    
                } else {
                    eachSubstring.matched = false
                }
            } else {
                eachSubstring.matched = false
            }
        }
        
        if eachContained == targetString[targetString.startIndex] {
            let substring = Substring(content: String(eachContained), range: characterIndex...characterIndex)
            substrings.append(substring)
        }
    }
    
    return substrings.filter({$0.matched == true}).map({$0.range})
}


let ranges = findString(targetString, inString: string)

for each in ranges {
    print(string[each])
}