LeetCode之“數學”：Happy Number

標籤：

　　題目連結

　　題目要求：

　　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.

　　這道題比較需要注意的一點是要在合適的時候跳出死迴圈。程式如下：

 1 class Solution { 2 public: 3     bool isHappy(int n) { 4         vector<int> vec; 5         vec.push_back(n); 6         while(n!= 1) 7         { 8             int sum = 0; 9             int tmpN = n;10             while(tmpN != 0)11             {12                 sum += (tmpN % 10) * (tmpN % 10);13                 tmpN /= 10;14             }15             n = sum;16             17             if(find(vec.begin(), vec.end(), n) != vec.end())18                 break;19             else20                 vec.push_back(n);21         }22         23         return n == 1;24     }25 };

 

LeetCode之“數學”：Happy Number