202. 快乐数

  1. func isHappy(n int) bool {
  2.     slow, fast := n, next(n)
  4.     for fast != 1 && fast != slow {
  5.         slow = next(slow)
  6.         fast = next(next(fast)) // 1的各位平方和还是1, 所以不会跳过
  7.     }
  9.     return fast == 1
  10. }
  12. func next(n int) int {
  13.     sum := 0
  14.     for n > 0 {
  15.         sum += (n % 10) * (n % 10)
  16.         n /= 10
  17.     }
  19.     return sum 
  20. }