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

• 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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