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 };