[LeetCode]Happy Number

標籤：

Happy Number

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

 

問題在於判斷是否進入迴圈，可以用Hash table記錄出現過的數字，當再次出現，則進入迴圈。和Fraction to Recurring Decimal問題類似。

 1 class Solution { 2 public: 3     bool isHappy(int n) { 4         unordered_set<int> showed; 5         if(n<1) 6         { 7             return false; 8         } 9         if(n==1)10         {11             return true;12         }13         int s;14         while(true)15         {16             s=0;17             while(n!=0)18             {19                 s+=(n%10)*(n%10);20                 n/=10;21             }22             if(s==1)23             {24                 return true;25             }26             else if(showed.find(s)!=showed.end())27             {28                 return false;29             }30             showed.insert(s);31             n=s;32         }33     }34 };

 

[LeetCode]Happy Number