func sqr(x int) int {
	return x * x
}

func isHappy(n int) bool {
	occur := make(map[int]struct{})
	for {
		if _, ok := occur[n]; ok {
			return false
		} else if n == 1 {
			return true
		}
		occur[n] = struct{}{}
		var next int
		for next = 0; n != 0; n /= 10 {
			next += sqr(n % 10)
		}
		n = next
	}
	return false
}