import Foundation
/*
extractDigits
-------------
Walks through the input string and collects only characters
that are recognized as digits.
Swift's Character.isNumber provides Unicode‑aware digit detection.
The function uses a simple and efficient filter operation
followed by String construction.
*/
func extractDigits(_ s: String) -> String {
// Filter characters that are digits and build a new string
let digits = s.filter { $0.isNumber }
return String(digits)
}
//
// Main execution
//
let str = "5 rustc#8go 9001 c c++ 17python"
// Extract digits
let digits = extractDigits(str)
// Display results
print("Original: \(str)")
print("Digits: \(digits)")
/*
run:
Original: 5 rustc#8go 9001 c c++ 17python
Digits: 58900117
*/
