【leetcode】【202】Happy Number

一、問題描述

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

二、問題分析

比較簡單的一道題，唯一需要注意的一點就是，如何判斷產生了loop？產生loop無非就是新的sum與之前的某個sum相等唄。因此需要一個存儲結構，需要保證sum值的唯一性。在java容器裏有set恰好符合。

三、Java AC代碼

public boolean isHappy(int n){
		int res = n;
		HashSet<Integer> hashSet = new HashSet<Integer>();
		if (n<=0) {
			return false;
		}
		while(res!=1){
			if (hashSet.contains(res)) {
				return false;
			}else {
				hashSet.add(res);
			}
			res = squareSums(res);
		}
		return true;
	}
	int squareSums(int x){
		int res = 0;
		while(x!=0){
		    int tmp = x % 10;
			res += tmp*tmp;
			x /= 10;
		}
		return res;
	}