import Foundation
func removeNonCommonLetters(_ word1: String, _ word2: String) -> String {
let filtered = word1.filter { word2.contains($0) }
return String(filtered)
}
let word1 = "forest"
let word2 = "tor"
let result = removeNonCommonLetters(word1, word2)
print(result)
/*
run:
ort
*/