202. Happy Number

难度: Easy

题目描述

Write an algorithm to determine if a number n is happy.

A happy number is a number defined by the following process:

• Starting with any positive integer, replace the number by the sum of the squares of its digits.
• Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1.
• Those numbers for which this process ends in 1 are happy.

Return true if n is a happy number, and false if not.

 

Example 1:

Input: n = 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

Example 2:

Input: n = 2
Output: false

 

Constraints:

• 1 <= n <= 231 - 1

解题思路

代码实现

解决方案

java

func isHappy(n int) bool {

	slow, fast := n, step(n)
	for fast != 1 && slow != fast {
		slow = step(slow)
		fast = step(step(fast))
	}
	return fast == 1

}

func step(n int) int {

	if n < 10 {
		return n * n
	}
	return step(n/10) + step(int(n)%10)
}