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struct WordMap {
    let string:String
    var indexes:[String:[Int]]
    let substrs:[String]
    let substrset:Set<String>
    
    init(string:String, substrs:[String]){
        self.string = string
        self.substrs = substrs
        self.indexes = [String:[Int]]()
        let chars = Array(string.characters)
        //easy to access set of substrs you want to map
        self.substrset = Set<String>(substrs)
        
        let length = self.string.characters.count
        
        //initialize index map
        for elem in self.substrs {
            self.indexes[elem] = [Int]()
        }
        
        
        //repeating loop to get substr indexes
        for phrase in self.substrs {
            var substart = 0
            var subend = phrase.characters.count-1
            //intermediate loop to cut substrs of specific sizes
            while subend < length {
                let slice = String(chars[substart...subend])
                if slice == phrase {
                    self.indexes[slice]!.append(substart)
                }
                substart += 1
                subend += 1
            }
        }
    }
    
    //gets the indexes at which a word appears in a body of text
    func getIndexes(string:String) -> [Int] {
        return self.indexes[string]!
    }
}

let test = WordMap(string:"hello fine sire how are you today? we missed you", substrs: ["you", "sir"])
test.indexes
//["you": [24, 45], "sir": [11]]