I have submitted the code, the same code runs fine under my machine but it gives Test: #1, time: 124 ms., memory: 0 KB, exit code: 1, checker exit code: 0, verdict: RUNTIME_ERROR

/*
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 * and open the template in the editor.
 */
package algorithms;

import java.util.Scanner;

/**
 *
 * @author Naved Momin<[email protected]/[email protected]>
 */


public class SimpleMath {
    
    class Node{
    char data;
    
    Node left, right;
    }
    
    String data,op = "";
    
    Node root;
    public void ALGO( ){
        Scanner s = new Scanner(System.in);
        data = s.nextLine();
        if( checker() == -1 )
            System.out.println( data );
        else
        {
            mkTree();
            traverseTreeInorder(root);
            op = op.substring(0, op.length()-1);
            System.out.println(op);
        }
    }
    
    int checker( ){
        return data.indexOf("+");
    }
    
    public static void main(String[] args) {
        // TODO code application logic here
        new SimpleMath().ALGO();
    }

    private void mkTree() {
        char[] toCharArray = data.toCharArray();
        for (char c : toCharArray) {
            if( c != '+'){
                tree( c );
            }
        }
    }

    private void traverseTreeInorder(Node r) {
        if( r != null ){
            traverseTreeInorder(r.left);
            op = op + r.data + "+";
            traverseTreeInorder(r.right);
        }
    }

    private void tree(char c) {
        if( root == null ){
            root = new Node();
            root.data = c;
        }else{
            Node r,p;
            r = p = root;
            int i,j;
            i = (int)c;
            while (r != null ) {                
                p = r;
                
                
                j = (int)r.data;
                if(  i < j )
                    r = r.left;
                else
                    r = r.right;
            }
            r = new Node();
            r.data = c;
            i = (int)r.data;
            j = (int)p.data;
            if( i < j )
                p.left = r;
            else
                p.right = r;
            
        }
    }
}