# 202. Happy Number
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:
1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1
# Solution
Approach 1: Iteration -- use a set to deduplicate, or use Floyd cycle detection algorithm as seen in linked list cycle problem.
# Code (Python)
Approach 1:
class Solution:
def isHappy(self, n: int) -> bool:
history = set()
current = n
while current != 1 and current not in history:
history.add(current)
current = self.calc(current)
if current == 1:
return True
return False
def calc(self, num):
total = 0
while num:
total += (num % 10) ** 2
num = num // 10
return total
# Code (C++)
Approach 1:
class Solution {
public:
bool isHappy(int n) {
unordered_set<int> visited;
while (n != 1)
{
if (visited.find(n) != visited.end()) return false;
visited.insert(n);
int nextNum = 0;
while (n > 0)
{
int tmp = n % 10;
nextNum += tmp * tmp;
n = n / 10;
}
n = nextNum;
}
return true;
}
};