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 = 8282 + 22 = 6862 + 82 = 10012 + 02 + 02 = 1Credits: Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.
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思路:找规律，如果不是开心数，则后面会循环出现某个数。
public class Solution { public boolean isHappy(int n) { int sum = 0; int t = n; boolean isHappy = true; HashSet<Integer> set = new HashSet<>(); set.add(n); while (n != 1) { while (n > 0) { sum = sum + (n % 10) * (n % 10); n = n / 10; } n = sum; sum = 0; if (set.contains(n)) { isHappy = false; break; } set.add(n); } return isHappy; } }