202. Happy Number

题目摘要
判断一个正整数是否是“Happy Number”。
不断将正整数各位平方和相加，知道该正整数开始重复，如果重复为1，则是“Happy Number”。

解法
用Floyd环检测算法循环n，知道n开始出现重复，如果此时n = 1，则是“Happy Number”。

public class Solution {    public boolean isHappy(int n) {        int slow = n;        int fast = figure(slow);        while (slow != fast) {            slow = figure(slow);            fast = figure(fast);            fast = figure(fast);        }        return slow == 1 ? true : false;    }    public int figure(int n) {        int result = 0;        while (n > 0) {            result += Math.pow(n % 10, 2);            n /= 10;        }        return result;    }}

注意

• 用Floyd环检测法

可问问题

• 整数类型、范围

原题
Write an algorithm to determine if a number 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, and 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 numbers.

Example: 19 is a happy number

12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1