Unique Characters in Swift

uniquecharacter.swift

let string : String = "Hello, World!"
let uniqueString : String = "He1lo, W0r|d!"

func uniquecharacter(input: String) -> Bool
{
    
    var isUnique: Bool = true;
    let characters = Array(input.characters)
    var sortedCharacters = characters.sort()
    for var i: Int = 0; i < sortedCharacters.count; i++
    {
        
        let character = sortedCharacters[i]
        sortedCharacters.removeAtIndex(i)
        for var y : Int = 0; y < sortedCharacters.count; y++
        {
            
            let anotherCharacter = sortedCharacters[y]
            if character == anotherCharacter {
                print(character)
                print(anotherCharacter)
    
                isUnique = false;
                return isUnique;
            }
            else {
               sortedCharacters.removeAtIndex(i)
            }
        }
    }
    return isUnique
}

uniquecharacter(string); // false
uniquecharacter(uniqueString); // true