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

思路分析：這題比較簡單，就是不斷的做各個位置數位平方加和操作，看是否會產生1。但是有一個地方要注意，就是怎麼判斷出現了迴圈，這裡定義了一個Set，儲存所有出現過的數字，對於計算得到的新的和，如果沒有在Set中出現，就添加到Set中繼續進行平方求和；否則，就是遇到了已經出現的數字，出現了迴圈，可以直接結束迴圈，返回false。

AC Code

public class Solution {public boolean isHappy(int n) {    HashSet<Integer> appearedNums = new HashSet<Integer>();    while(!appearedNums.contains(n)){        appearedNums.add(n);        int sum = 0;        while(n != 0){            int digit = n % 10;            n /= 10;            sum += Math.pow(digit,2);        }        n = sum;        if(sum == 1) return true;    }    return false;    }}

LeetCode Happy Number