1、題目

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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

Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.

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2、分析

這個題目每次會把每位的平方相加，然后循環這樣，然后知道這個數字等于1為止，經過我們舉例分析，如果不是快樂數最終或者中途出現這些數字，最後都會進入 4 → 16 → 37 → 58 → 89 → 145 → 42 → 20 → 4 的循環中

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3、代碼實現

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public class Solution {public boolean isHappy(int n) {if (n <= 0)return false;int result = 0;while (n != 0) {int temp = n % 10;result += temp * temp;n = n / 10;}if (result == 1) return true;else if (result == 4 || result == 16 || result == 37 || result == 58 || result == 89 || result == 145 || result == 42 || result == 20 )return false;else return isHappy(result);} }

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