1 class Solution { 2 public: 3 bool isHappy(int n) { 4 int last = n; 5 6 unordered_set<int> exist; 7 8 do { 9 int sum = 0; 10 exist.insert(last); 11 while (last) { 12 int digit = last % 10; 13 sum += digit * digit; 14 last /= 10; 15 } 16 if (sum == 1) { 17 return true; 18 } 19 last = sum; 20 } while (exist.count(last) < 1); 21 return false; 22 } 23 };
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