[LeetCode]Happy Number

最新推荐文章于 2019-02-27 16:56:04 发布

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本文介绍了一种用于判断一个正整数是否为快乐数的算法。快乐数是指通过反复将其每位数字的平方相加，最终能得到1的数字。文章提供了一个使用C++实现的例子，该例子利用哈希集合来避免无限循环。

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
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分析：如果不是Happy Number的话，在计算过程中会出现loop。所以我们采用一组set来监测是否有loop。

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