Leetcode：202. Happy Number（JAVA）

【问题描述】

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】
每次的结果存到HashSet中，若存在则说明出现环路return false，直到计算出为1时return true。

public class Solution {
public boolean isHappy(int n) {
long ln = n;
Set<Long> set = new HashSet<Long>();

while (n < Integer.MAX_VALUE) {
if (set.contains(ln)) {
return false;
} else {
set.add(ln);
}
ln = digitSquare(ln);
if (ln == 1) {
return true;
}
}
return false;
}

private long digitSquare(long ln) {
long sum = 0;
while (ln != 0) {
sum += Math.pow(ln % 10, 2);
ln /= 10;
}
return sum;
}
}