LeetCode之Happy Number

1、题目

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

这个题目每次会把每位的平方相加，然后循环这样，然后知道这个数字等于1为止，经过我们举例分析，如果不是快乐数最终或者中途出现这些数字，最後都会进入 4 → 16 → 37 → 58 → 89 → 145 → 42 → 20 → 4 的循环中

3、代码实现

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);
}
}