leetcode之Happy Number

標籤：

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

這道題很簡單，思路大致如下，首先取這個數的每一位元，其次考慮到終止條件是1或者迴圈

最開始只判斷了最終條件如果是1就結束的情況，忘記了如果無限迴圈會怎麼樣，於是沒有AC。

從網上尋找了一下資料，發現用HashSet 是比較合理的，首先add()方法會將不在集合中的元素加入，其次contain()方法會判斷某個數是否在集合內，

因此寫了兩個函數，一個是得到下一個要判斷的數，另一個是判斷這個數是不是Happy Number

代碼如下：

public class Solution {    public boolean isHappy(int n) {        HashSet<Integer> hash = new HashSet<Integer>();        while (n != 1) {            if (hash.contains(n)) {                return false;            }            hash.add(n);            n = s(n);        }        return true;    }    public int s(int n){int num = 0;        while(n!=0){        int u = n/10;        int v = n%10;        n = u;        num += v*v;        }        int result = num;        return result;}}

　　

leetcode之Happy Number