How to go through the elements of type string

Question

I am writing a function that should return the number of duplicates. I can’t understand how to go through the elements of type string.

func countDuplicates(_ s:String) -> Int {
    var duplicates = 0

    for i in s {
        duplicates += 1
    }

    return duplicates
}

Answer 1

You can try:

func countDuplicates(_ s:String) -> Int {
    return s.count - Set(s).count
}

Where:

s.count // total number of characters
Set(s).count // number of unique characters