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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
问题在于判断是否进入循环，可以用Hash table记录出现过的数字，当再次出现，则进入循环。和Fraction to Recurring Decimal问题类似。
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 };
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原文地址：http://www.cnblogs.com/Sean-le/p/4736820.html
