202. Happy Number

chuandalishuo

于 2016-10-20 07:23:00 发布

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分类专栏： Leetcode easy 数字串处理文章标签： Leetcode easy

本文链接：https://blog.youkuaiyun.com/chuandalishuo/article/details/52867384

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本文介绍了一种用于判断任意正整数是否为快乐数的算法。快乐数是指通过反复替换为各位数字平方和的过程最终能够得到1的数字。文章提供了一个具体的例子来说明这一过程，并附带了完整的Java实现代码。

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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

public class Solution {
    public boolean isHappy(int n) {
        if(n<0) return false;
        List<Integer> nums = new ArrayList<>();
        nums.add(n);
        n = helper(n);
        while(n!=1){
            if(nums.contains(n)) return false;
            else nums.add(n);
            n = helper(n);
        }
        return true;
    }
    public int helper(int n){
        int result=0;
        while(n>0){
            result+=Math.pow(n%10,2);
            n/=10;
        }
        return result;
    }
}