开心数字

原题

　　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

 

 

题目大意

　　对任意一个正整数，不断求个数位上数字的平方和，若最终收敛为1，则该数字为happy number，不然程序可能从某个数开始陷入循环。

解题思路

　　对这个数字的每一个数位求平方和，若是如和为1或者平方和是以前出现过的就不进行求和，根据最后的结果判断是否是一个开心数字。

代码实现

算法实现类

mport java.util.HashSet;

public class Solution {
    public boolean isHappy(int n) {
        if (n < 1) {
            return false;
        }

        // 用于保存中间出现的结果
        HashSet<Integer> set = new HashSet<>(32);

        int tmp;
        int newN;

        // n不为1，而且n的值不能重复出现，不然会死循环
        while (n != 1 && !set.contains(n)) {
            set.add(n);
            newN = 0;
            while (n > 0) {
                tmp = n % 10;
                n /= 10;
                newN += tmp * tmp;
            }

            n = newN;
        }

        return n == 1;
    }
}