【Leetcode】Happy Number

题目链接：https://leetcode.com/problems/happy-number/

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

思路：

如果计算结果中出现4或它自身，则不是快乐数。

算法：

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plain copy

1. public boolean isHappy(int n) {
2. char c[] = String.valueOf(n).toCharArray();
3. int sum = 0;
4. for (char t : c) {
5. int x = Integer.parseInt(String.valueOf(t));
6. sum += x * x;
7. }
8. if (sum == 1) {
9. return true;
10. } else if (sum == 4 || sum == n)
11. return false;
12. else if (isHappy(sum))
13. return true;
14. return false;
15. }