[leetcode] 202. Happy Number

標籤：

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

Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.

[Solution]

不是happy number的話，結果會出現迴圈，用set記錄所有結果，出現重複則為false

 1 bool isHappy(int n) 2     { 3         set<int> table; 4          5         table.insert(n); 6         while (1) 7         { 8             int k = 0; 9             while (n)10             {    11                 k += (n % 10) * (n % 10);12                 n /= 10;13             }14             if (k == 1)15                 return true;16             if (table.find(k) != table.end())17                 return false;18             n = k;19             table.insert(n);20         }21     }

 

[leetcode] 202. Happy Number