LeetCode Happy Number

Description:

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

Solution:

默认了一个条件：所有的数字，将他的各个位数平方和带入的循环，是一个有限循环。

import java.util.*;public class Solution {public boolean isHappy(int n) {HashSet<Integer> set = new HashSet<Integer>();set.add(n);int temp = 0, ones;while (true) {temp = 0;while (n > 0) {ones = n % 10;n /= 10;temp += ones * ones;}n = temp;if (n == 1)return true;if (set.contains(n))break;set.add(n);}return false;}}