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题目：
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
分析：
这道题的难点还是读题呀，又没有看懂题目的需求
题目要求对任意一个正整数，不断各个数位上数字的平方和，若最终收敛为1，则该数字为happy number，否则程序可能从某个数开始陷入循环。
这道题目我们只用根据规则进行计算，使用Hashset来存储结果，这样就可以判断结果是不是陷入循环了
代码：
public boolean isHappy(int n) { if(n<=0){ return false; } long lnResult = n; Set<Long> set = new HashSet<Long>(); while(lnResult<=Integer.MAX_VALUE) { lnResult = digitSquare(lnResult); if(lnResult == 1){ return true; } if(set.contains(lnResult) ){ return false; } else{ set.add(lnResult); } } return false; } private long digitSquare(long lnInput) { long Sum = 0; while(lnInput!=0) { Sum += Math.pow(lnInput%10, 2); lnInput /= 10; } return Sum; }
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原文地址：http://www.cnblogs.com/savageclc26/p/4897352.html
