火车编组

　　其实就是栈操作能否按照给定顺序输出

 public static String getResult(int[] res){
        if (res.length <= 2){
            return "Yes";
        }
        Deque<Integer> de = new LinkedList<>();
        int s = 1;
        int k = res[0];
        de.push(1);
        boolean[] flag = new boolean[res.length];
        while (de.peek() != k){
            flag[s-1] = true;
            de.push(++s);
        }
        for (int i = 0; i < res.length; i++) {
            int t = res[i];
            if (de.isEmpty()){
                de.push(t);
                flag[t-1] = true;
            }else if (t == de.peek()){
                de.pop();
            }else {
                if (flag[t-1]){
                    return "No";
                }
                de.push(t);
                flag[t-1] = true;
            }

        }

        return "Yes";



    }