5 Happy Number

最新推荐文章于 2021-06-29 17:45:10 发布

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最新推荐文章于 2021-06-29 17:45:10 发布

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分类专栏：做算法防痴呆

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本文介绍了一种用于判断正整数是否为快乐数的算法。快乐数是指通过将该数替换为其各位数字平方和并重复这一过程，最终能够得到1的正整数。文章提供了两种实现方法：一种使用循环重复计算直至达到1或确定陷入无限循环；另一种采用哈希集合避免重复计算，提高效率。通过示例输入19验证了算法的有效性。

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Write an algorithm to determine if a number n 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.

Return True if n is a happy number, and False if not.

Example:

Input: 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

C++代码

class Solution {
    int f(int n){
        int sum = 0;
        while(n){
            int digit = n%10;
            n/=10;
            sum += digit * digit;
        }
        return sum;
    }
    
public:
    bool isHappy(int n) {
        for(int rep=0; rep<19; ++rep){
            n = f(n);
            if(n == 1){
                return true;
            }
        }
        return false;
    }   
};

class Solution{
    int f(int n){
        int sum = 0;
        while(n){
            int digit = n % 10;
            n /= 10;
            sum += digit * digit;
        }
        return sum;
    }
public:
    bool isHappy(int n){
        unordered_set<int> visited;
        while(true){
            if(n == 1){
                return true;
            }
            n = f(n);
            if(visited.count(n) == 1){
                return false;
            }
            visited.insert(n);
        }
    }
}