LeetCode in Kotlin
202. Happy Number
Easy
Write an algorithm to determine if a number n 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.
- 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.
Return true if n is a happy number, and false if not.
Example 1:
Input: n = 19
Output: true
Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1
Example 2:
Input: n = 2
Output: false
Constraints:
1 <= n <= 231 - 1
Solution
class Solution {
private val set = mutableSetOf<Int>()
tailrec fun isHappy(n: Int): Boolean {
var num = n
var squareSum = 0
while (num > 0) {
val digit = num % 10
squareSum += digit * digit
num /= 10
}
if (squareSum == 1) {
return true
}
if (set.contains(squareSum)) {
return false
}
set.add(squareSum)
return isHappy(squareSum)
}
}