力扣-202题快乐数（C++）- 哈希

电玩女神 2022-09-07 14:59 178阅读 0赞

题目链接：[https://leetcode-cn.com/problems/happy-number/][https_leetcode-cn.com_problems_happy-number]  
题目如下：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70 1]

class Solution {
        
    public:
        int calculate_sum(int num){
        
            int result=0;
    
            while(num!=0){
        
                int number=num%10;
                result+=number*number;
                num=num/10;
            }
    
            return result;
        }
    
        bool isHappy(int n) {
        
            //if(n==1) return true;
            //注：题目中的无限循环，即求和的过程中，sum会重复出现
            //当遇到要快速判断一个元素是否出现集合里的时候，考虑哈希法
            
            unordered_set<int> uset;
    
            int num=calculate_sum(n);
    
            while(1){
        
    
                if(uset.count(num)!=0) return false;
                else uset.insert(num);
    
                if(num==1) return true;
                num=calculate_sum(num);
            }
            
        }
    };

[https_leetcode-cn.com_problems_happy-number]: https://leetcode-cn.com/problems/happy-number/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70]: /images/20220829/e93b5fa4190942ae8c2fdecf0fd13edf.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNDY3Njcw_size_16_color_FFFFFF_t_70 1]: /images/20220829/8b9fed64a73a4093bc041dcdec78c345.png