class Solution {
    func firstUniqChar(_ s: String) -> Int {
        let noRepeat = Set(s)
        var onlyAppearOnceLetterIndex = [Int]()
        for char in noRepeat{
            if s.filter({ $0 == char }).count == 1 {
                let charIndex = s.index(of: char)!.encodedOffset
                onlyAppearOnceLetterIndex.append(charIndex)
            }
        }

        return onlyAppearOnceLetterIndex.isEmpty ? -1 : onlyAppearOnceLetterIndex.min()!

    }
}