Implement an algorithm to determine if a string has all unique characters.

uniqueChar.swift

import Cocoa

struct Counter {
    var table =  Dictionary<String,Int>()
    
    mutating func insertUnique(_ word: String) -> Bool {
        let value = table[word] ?? 0
        guard value == 0 else { return false }
        table[word] = value + 1
        return true
    }
}

func uniqueCharacters(_ word: String) -> Bool {
    var counter = Counter()
    for w in word {
        if !counter.insertUnique(String(w)) {
            return false
        }
    }
    return true
}

print(uniqueCharacters("abcdefghi"))
print(uniqueCharacters("abcdefghii"))