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HappyNumber.java
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HappyNumber.java
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/*
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:
Input: 19
Output: true
Explanation:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
*/
class Solution {
public boolean isHappy(int n)
{
return helper(n, new HashSet<Integer>());
}
public boolean helper(int n, Set<Integer> set)
{
if (n == 1)
{
return true;
}
else if (set.contains(n))
{
return false;
}
set.add(n);
int sum = 0;
while (n > 0)
{
int remainder = n % 10;
sum += remainder * remainder;
n /= 10;
}
return helper(sum, set);
}
}