202. Happy Number

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

没什么trick，找题目要求做即可.

public class Solution {
　　public boolean isHappy(int n) {
　　　　Set<Integer> set = new HashSet<>();
　　　　int next = n;
　　　　while (!set.contains(next)) {
　　　　　　set.add(next);
　　　　　　n = next;
　　　　　　next = 0;
　　　　　　while (n > 0) {
　　　　　　　　next += (n % 10) * (n % 10);
　　　　　　　　n /= 10;
　　　　　　}
　　　　　　if (next == 1) {
　　　　　　　　return true;
　　　　　　}
　　　　}
　　　　return false;
　　}
}

原文：http://www.cnblogs.com/shini/p/4446969.html