题解 | #点击消除#

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Iterator;
import java.util.Scanner;
import java.util.Arrays;


// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {

    private static final Deque<Character> stack = new ArrayDeque<>();
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String str = in.next();

        for (int i = 0; i != str.length(); ++i) {
            if (stack.isEmpty() || stack.peek() != str.charAt(i)) {
                stack.push(str.charAt(i));
            } else {
                stack.pop();
            } 
        }

        if (stack.isEmpty()) {
            System.out.println("0");
        } else {
                    StringBuilder sb = new StringBuilder();
            for (char x : stack) {
                sb.append(x);
            }
            sb.reverse();
            System.out.println(sb.toString());
        }        
    }
}