0202. Happy Number
https://leetcode.com/problems/happy-number
Description
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
ac
class Solution {
public boolean isHappy(int n) {
// edge cases
if (n <= 0) return false;
return recur(n, new HashSet<Integer>());
}
private boolean recur(int n, Set<Integer> set) {
// exit
if (n == 1) return true;
if (set.contains(n)) return false; // meet loop
set.add(n);
int m = 0;
while (n > 0) {
m += Math.pow(n % 10, 2);
n /= 10;
}
// next
return recur(m, set);
}
}
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