leetcode 202. Happy Number

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;
    }
};