import Foundation
// A happy number is a number that eventually reaches 1
// when repeatedly replaced by the sum of the squares of its digits.
//
// 19 = 1^2 + 9^2 = 82
// 19 -> 82 -> 68 ->100 -> 1 eventually reaches 1
// 19 = happy numbe
// Compute the sum of squares of digits of n
func sumOfDigitSquares(_ n: Int) -> Int {
var num = n
var sum = 0
while num > 0 {
let d = num % 10
sum += d * d
num /= 10
}
return sum
}
// Determine whether n is a happy number
func isHappy(_ n: Int) -> Bool {
var seen = Set<Int>()
var num = n
while num != 1 && !seen.contains(num) {
seen.insert(num)
num = sumOfDigitSquares(num)
}
return num == 1
}
func main() {
let a = 1
let b = 100
var happyNumbers: [Int] = []
for i in a...b {
if isHappy(i) {
happyNumbers.append(i)
}
}
print("Happy numbers in range [\(a), \(b)]:")
print(happyNumbers.map(String.init).joined(separator: " "))
}
main()
/*
run:
Happy numbers in range [1, 100]:
1 7 10 13 19 23 28 31 32 44 49 68 70 79 82 86 91 94 97 100
*/
