题目：

题解：

func isHappy(n int) bool {
    cycle := map[int]bool{4: true, 6: true, 37: true, 58: true, 89: true, 145: true, 42: true, 20: true}
    for n != 1 && !cycle[n] {
        n = step(n)
    }
    return n == 1
}

func step(n int) int {
    sum := 0
    for n > 0 {
        sum += (n%10) * (n%10)
        n = n/10
    }
    return sum
}