Leetcode/202.HappyNumber.h at master · bluepp/Leetcode · GitHub

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/*
  2015-06-15
  bluepp
  May the force be with me!

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

https://leetcode.com/problems/happy-number/
*/

    bool isHappy(int n) {
        unordered_set<int> set;
        string ss = to_string(n);

        while (1) {
            int accum = 0;

            for (auto p : ss) {
                int t = p-'0';
                accum += t*t;
            }

            if (accum == 1) {
                return true;
            } else if (set.count(accum)) {
                return false;
            } else {
                set.insert(accum);
                ss = to_string(accum);
            }
        }

        return false;
    }


/* -------------------------------------------------------- */


    bool isHappy(int n) {

       set <int> s;

       while (n != 1)
       {
           int t = 0;

           while (n)
           {
               t += (n % 10) * (n % 10);
               n /= 10;
           }

           n = t;
           if (s.count(n)) break;
           else s.insert(n);
       }

       return n == 1;
    }


/* https://leetcode.com/discuss/101005/4-c-solutions-with-explanations */

    bool isHappy(int n) {

        unordered_set<int> tmp;

        while(n != 1)
        {
            if(tmp.find(n) == tmp.end())
                tmp.insert(n);
            else
                return false;

            int sum = 0;
            while(n != 0)
            {
                sum += pow(n % 10, 2);
                n = n / 10;
            }

            n = sum;
        }

        return true;
    }