【leetcode】【easy】202. Happy Number

202. 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: 

Input: 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1

题目链接：https://leetcode.com/problems/happy-number/

解法：hash

class Solution { public: bool isHappy(int n) { if (n<0) return false; unordered_set<int> record; while(true){ int tmp = cal(n); if(tmp == 1) return true; if(record.find(tmp) != record.end()) return false; record.insert(tmp); n = tmp; } } int cal(int n){ int res = 0; while (n>0){ res += pow(n%10, 2); n = int(n/10); } return res; } };