[刷题防痴呆] 0202 - 快乐数 (Happy Number

题目地址

https://leetcode.com/problems/happy-number/description/

题目描述

202. Happy Number

Write an algorithm to determine if a number n 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.

Return True if n is a happy number, and False if not.

思路

• 用hashset来看看变换的过程中有没有环. 即, 有没有重复的数.
• 如果出现重复, 则不是快乐数.

关键点

代码

• 语言支持：Java

class Solution {
    public boolean isHappy(int n) {
        Set<Integer> set = new HashSet<>();
        while (n != 1) {
            if (set.contains(n)) {
                return false;
            }
            set.add(n);
            n = getNext(n);
        }

        return true;
    }

    private int getNext(int n) {
        int sum = 0;
        while (n != 0) {
            int cur = n % 10;
            sum += cur * cur;
            n /= 10;
        }

        return sum;
    }
}