202. Happy Number（LeetCode）

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

   1 class Solution {
   2 public:
   3    int fang(int n)
   4     {
   5         int sum = 0;
   6         while (n != 0)
   7         {
   8             sum += (n % 10)*(n % 10);
   9             n = n / 10;
  10         }
  11         cout<<sum<<endl;
  12         return sum;
  13     }
  14
  15     bool isHappy(int n) {
  16         int i=0;
  17             while (n!=1&&i<100)
  18             {
  19                 n = fang(n);
  20                 cout<<n<<endl;
  21                 i++;
  22             }
  23             if (n == 1&&i<100)
  24             {
  25                 return true;
  26             }
  27             if (i >= 100)
  28             return false;
  29     }
  30 };

   1 class Solution {
   2 public:
   3     bool isHappy(int n) {
   4         unordered_map<int, bool> m;
   5         while (n != 1 && !m.count(n)){
   6             m[n] = true;
   7             int new_n = 0;
   8             while (n){
   9                 new_n += (n % 10)*(n % 10);
  10                 n /= 10;
  11             }
  12             n = new_n;
  13         }
  14         return n == 1;
  15     }
  16 };