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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
题目也是比较简单，AC代码如下：
bool isHappy(int n) { if(n<=0) return false; else if(n==1) return true; else { int squSum=n; int LUT[10]; for(int i=0;i<10;i++) LUT[i] = i*i; vector<int> sum; while(squSum!=1) { sum.push_back(squSum); int tmp=squSum; squSum=0; while(tmp>=10) { squSum=squSum+LUT[tmp%10]; tmp=tmp/10; } squSum=squSum+LUT[tmp]; if(squSum == 1) return true; vector<int>::iterator result = find( sum.begin( ), sum.end( ), squSum); if(result != sum.end()) break; } return false; } }
注意下，用到了查找表，能省点时间就省点吧。
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原文地址：http://www.cnblogs.com/ww-jin/p/4448408.html
