leetcode - happy number

leetcode - happy number

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

 

class Solution {
public:
    bool isHappy(int n) {
        int hashtable[800];
        //vector<int> iter;
        memset(hashtable, -1, sizeof(hashtable));//initilize all elements as -1;
        int sum=0;
        //int it=0;
        
        while(hashtable[getsum(n)]== -1){
            sum = getsum(n);
            hashtable[sum] = 1;
            //if(iter.find(n)!= n.pos) return 0;
            //iter.push_back(n);
            
            if(sum == 1) return 1;
            else n = sum;
        }
        return 0;
    }
    
    int getsum(int n){
            int nn = n;
            int sum = 0;
            while(nn>0){
                int tp = nn%10;
                nn = nn/10;
                sum = sum + tp*tp;
            }
            return sum;
    }
};

好纠结。……又是hashtable……

之前想的是建一个数组，相当于对每个数有一个标志，那么数组维度应该是10^9. 但是不知道为什么对输入为1 这个case老是runtime error。难道是数组太大？

后来看了一下网上的，说是只需要9*9*9<800维数组就可以。但是其实思路和我的基本一样。不知道我的那个错在哪里……