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:
Input: 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1
就是用个Set来检查是否出现 endless loop。
class Solution { public: bool isHappy(int n) { set<int> s; while(true) { int val = helper(n); if(val == 1) { return true; } if(s.find(val) != s.end()) // already found, return false; s.insert(val); n = val; } return false; } private: int helper(int n) { int res = 0; while(n!=0) { int v = n %10; n /= 10; res += v*v; } return res; } };
Mistakes:
又一次,栽在了while loop的条件上。
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