Str Str

    func strStr(_ haystack: String, _ needle: String) -> Int {
        guard needle.count > 0 else { return 0}
        guard haystack.count >= needle.count else { return -1}

        let arr1 = Array(haystack)
        let arr2 = Array(needle)
        var p1 = 0
        while p1 <= arr1.count - arr2.count {
            if arr1[p1] == arr2[0]{
                var p2 = 0
                var p = p1
                while p2 < arr2.count && arr1[p] == arr2[p2]{
                    p2 += 1
                    p += 1
                }
                if p2 == arr2.count {return p1}
            }
            p1 += 1
        }
        return -1
    }