[LeetCode] 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

思路：採用set儲存之前碰到過的數，藉此判斷是否出現迴圈

複雜度：

代碼：

public class Solution {    public boolean isHappy(int n) {        Set<Integer> set=new HashSet<Integer>();        return cycle(n, set);    }    public boolean cycle(int k,Set<Integer> set)    {        String sk=Integer.toString(k);        int sum=0;        for(int i=0;i<sk.length();i++)        {            sum+=(sk.charAt(i)-‘0‘)*(sk.charAt(i)-‘0‘);        }        if(sum==1) return true;        if(set.contains(sum)) return false;        set.add(sum);        return cycle(sum, set);    }}

 

最佳化：

擴充：

[LeetCode] Happy Number