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

  class Solution {
  public:
     int fang(int n)
      {
          int sum = 0;
          while (n != 0)
          {
              sum += (n % 10)*(n % 10);
              n = n / 10;
          }
          cout<<sum<<endl;
          return sum;
      }
      
      bool isHappy(int n) {
          int i=0;
              while (n!=1&&i<100)
              {
                  n = fang(n);
                  cout<<n<<endl;
                  i++;
              }
              if (n == 1&&i<100)
              {
                  return true;
              }
              if (i >= 100)
              return false;
      }
  };

  class Solution {
  public:
      bool isHappy(int n) {
          unordered_map<int, bool> m;
          while (n != 1 && !m.count(n)){
              m[n] = true;
              int new_n = 0;
              while (n){
                  new_n += (n % 10)*(n % 10);
                  n /= 10;
              }
              n = new_n;
          }
          return n == 1;
      }
  };