extension Collection { func unfoldSubSequences(limitedTo maxLength: Int) -> UnfoldSequence<SubSequence,Index> { sequence(state: startIndex) { start in guard start < self.endIndex else { return nil } let end = self.index(start, offsetBy: maxLength, limitedBy: self.endIndex) ?? self.endIndex defer { start = end } return self[start..<end] } } func subSequences(of n: Int) -> [SubSequence] { .init(unfoldSubSequences(limitedTo: n)) }
}
let numbers = "1234567"
let subSequences = numbers.subSequences(of: 2)
print(subSequences) // ["12", "34", "56", "7"]