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LeetCode Happy Number

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

1 ² + 9 ² = 82
8 ² + 2 ² = 68
6 ² + 8 ² = 100
1 ² + 0 ² + 0 ² = 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得到每一位数，相加进行判断。这里还用了一个set来存储已经出现的数字，如果重复了，说明就不是一个happy number。

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