leetcode 202. Happy Number

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原文链接：http://www.cnblogs.com/zywscq/p/5429123.html

本文介绍了一种用于判断一个正整数是否为快乐数的算法。快乐数是指通过反复替换该数为它每个位数的平方和的过程最终能够得到1的数字。文章提供了详细的算法实现过程及代码示例。

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

简单题。

class Solution {
public:
    bool isHappy(int n) {
        if(n==1) return true;
        set<long long int>st;
        st.insert(n);
        while(n!=1){
            int t=0;
            int tn=n;
            while(tn>0){
                t+=(tn%10)*(tn%10);
                tn/=10;
            }
            if(t==1) return true;
            if(st.count(t)>0){
                return false;
            }
            st.insert(t);
            n=t;
        }
        return true;
    }
};