设计getMin功能的栈

 public int[] getMinStack (int[][] op) {
        // write code here
        Stack<Integer> stack1 = new Stack<>();
        Stack<Integer> stack2 = new Stack<>();
        List<Integer> list = new ArrayList<>();
        for(int i=0;i<op.length;i++){
            if(op[i][0]==3){
                list.add(stack2.peek());
            }else if(op[i][0]==2){
                int a = stack1.pop();
                if(a==stack2.peek()) stack2.pop();
            }else{
                int temp = op[i][1];
                stack1.push(temp);
                //这里注意判断stack2是否为空
                if(stack2.isEmpty() || temp<=stack2.peek()) stack2.push(temp);
            }
        }
        int[] res = new int[list.size()];
        for(int i=0;i<list.size();i++){
            res[i] = list.get(i);
        }
        return res;
    }