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LeetCode Happy Number

来源：程序员人生发布时间：2015-06-23 08:16:23 阅读次数：3193次

1. 题目

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

2.解题方案

class Solution { public: bool isHappy(int n) { if(n < 1){ return false; } if(n == 1){ return true; } unordered_set<int> showNums; showNums.insert(n); while(true){ int sum = 0; while(n != 0){ int oneDigital = n % 10; n = n / 10; sum = sum + oneDigital * oneDigital; } if(sum == 1){ return true; }else{ if(showNums.find(sum) == showNums.end()){ showNums.insert(sum); }else{ return false; } } n = sum; } } };

思路：用求余和除以10得到每位数，相加进行判断。这里还用了1个set来存储已出现的数字，如果重复了，说明就不是1个happy number。

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