HappyNumberTwoPointer.java

/*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*/
import java.util.*;
class HappyNumberTwoPointer{
  public boolean isHappy(int n) {
    int slow=n;
    int fast=getNext(n);
    while(fast!=1 && slow!=fast){
      slow=getNext(slow);
      fast=getNext(getNext(fast));
    }
    return fast==1;
  }
  private int getNext(int n) {
    int sum=0;
    while(n>0){
      int d=n%10;
      sum+=d*d;
      n/=10;
    }
    return sum;
  }
  public static void main(String[] args){
    Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
    HappyNumberTwoPointer obj=new HappyNumberTwoPointer();
    System.out.print(obj.isHappy(n));  
  }
}