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 = 8282 + 22 = 6862 + 82 = 10012 + 02 + 02 = 1思路：把一个数每一位平方后加和得到一个新的数，然后继续对这个新的数做同样的操作。如果最后能得到一个1，则最原始的数就是一个”Happy Number”。如果在还没达到1的过程中出现循环，则这个数肯定不是。用到C++ 的set。set.count()判断一个数是否在set中，set.insert()，向set 中插入元素。INT_MAX，表示最大整数。
class Solution { public: bool isHappy(int n) { if(n==0) return false; set<long> s; while(n<=INT_MAX) { if(n==1) return true; if(s.count(n)>0) return false; s.insert(n); n=digitSquare(n); } return false; } long digitSquare(long num) { long r=0; int t=0; while(num) { t=num%10; r+=t*t; num/=10; } return r; } };
转载于:https://www.cnblogs.com/vincent93/p/6686637.html
