[LintCode] Happy Number 快乐数

Posted 2020-07-21 Grandyang

 

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

1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1

 

LeetCode上的原题，请参见我之前的博客Happy Number。

 

解法一：

class Solution {
public:
    /**
     * @param n an integer
     * @return true if this is a happy number or false
     */
    bool isHappy(int n) {
        set<int> s;
        while (n != 1) {
            int t = 0;
            while (n) {
                t += (n % 10) * (n % 10);
                n /= 10;
            }
            n = t;
            if (s.count(n)) break;
            else s.insert(n);
        }
        return n == 1;
    }
};

 

解法二：

class Solution {
public:
    /**
     * @param n an integer
     * @return true if this is a happy number or false
     */
    bool isHappy(int n) {
        while (n != 1 && n != 4) {
            int t = 0;
            while (n) {
                t += (n % 10) * (n % 10);
                n /= 10;
            }
            n = t;
        }
        return n == 1;
    }
};