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
1^2 + 9^2 = 82 8^2 + 2^2 = 68 6^2 + 8^2 = 100 1^2 + 0^2 + 0^2 = 1
这道题的做法是就是把一个正数不断求各个数位的平方和，如果得到了1，就返回true，否则把结果存在一个set里，如果一旦出现重复的数，说明不能得到1，所以不是happy number
public class Solution { /** * @param n an integer * @return true if this is a happy number or false */ public boolean isHappy(int n) { // Write your code here if(n <= 0) return false; if(n == 1) return true; HashSet<Integer> set = new HashSet<Integer>(); int num = n; while(!set.contains(num)){ set.add(num); int next = 0; while(num > 0){ next += (num % 10) * (num % 10); num /= 10; } if(next == 1) return true; else num = next; } return false; } }
原文：http://www.cnblogs.com/goblinengineer/p/5215662.html