LeetCode: 202. Happy Number

题目描述

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

解题思路

模拟。用 set 记录出现过的数字。

AC 代码

class Solution {
public:
    bool isHappy(int n) {
        set<int> record;

        while(true)
        {
            string numStr = to_string(n);
            record.insert(n);
            n = 0;

            for(size_t i = 0; i < numStr.size(); ++i)
            {
                n += pow(numStr[i]-'0', 2);
            }

            if(n == 1) return true;
            else if(record.find(n) != record.end()) return false;
        }
    }
};