POJ 2255 java

import java.io.BufferedInputStream;
import java.util.ArrayList;
import java.util.Scanner;

public class Main {

public static void main(String[] args) {
Main main = new Main();
main.run();
}

public static int num;// ?
public static char[] pre;
public static char[] in;
public static ArrayList aftList;

public static void run() {
Scanner sin = new Scanner(System.in);
while (sin.hasNext()) {
num = 0;
pre = sin.next().toCharArray();
in = sin.next().toCharArray();
aftList = new ArrayList();
// public static int num = 0;//?
ExeLeft(0, in.length - 1, '0');
aftList.trimToSize();
for (int i = 0; i < aftList.size(); i++) {
System.out.print(aftList.get(i));
}
System.out.println();