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
Solution：Hashset
思路： 看结果是否开始重复，或达到1
Time Complexity: .. Space Complexity: ..
Solution Code：
class Solution {
public boolean isHappy(int n) {
Set<Integer> inLoop = new HashSet<Integer>();
while (inLoop.add(n)) {
int squareSum = 0;
while (n > 0) {
int digit = n % 10;
squareSum += digit * digit;
n /= 10;
}
if (squareSum == 1)
return true;
else
n = squareSum;
}
return false;
}
}
