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

中规中矩的答案

bool isHappy(int n) {    unordered_map
     
       m;    while (m.find(n) == m.end())    {        m[n] = true;        int t = 0;        while (n)        {            int a = n % 10;            t += a * a;            n = n / 10;        }        n = t;    }    return n == 1;}