Happy Number

我就是我 2022-01-05 10:41 218阅读 0赞

题目描述：

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

以前一直是按时间顺序做的，从这题开始按难易程度做。

我的解法：

bool isHappy(int n) {
        if(n <= 0)
            return false;
        set<int> st;
        while (1)
        {
            int tmp = 0;
            while (n > 0)
            {
                tmp += (n % 10)*(n % 10);
                n /= 10;
            }
            if(tmp == 1)
                return true;
    
            else
            {
                if(st.find(tmp) != st.end())
                    return false;
                else
                    st.insert(tmp);
            }
            n = tmp;
        }
    }

简洁版：

bool isHappy(int n) {
        if(n <= 0)
            return false;
        unordered_set<int> st;
        while (n != 1 && st.find(n) != st.end())
        {
            st.insert(n);
            int tmp = 0;
            do 
            {
                tmp += (n % 10) * (n % 10);
            } while ( (n /= 10) > 0);
            n = tmp;
        }
        return n == 1;
    }

转载于:https://www.cnblogs.com/gattaca/p/4594675.html