包含min函数的栈、合并min函数的栈

定义栈的数据结构，请在该类型中实现一个能够得到栈中所含最小元素的min函数（时间复杂度应为O（1））。 

public class Solution {
    Stack<Integer> stacks1 = new Stack<>();
    Stack<Integer> stacks2 = new Stack<>();
    public  void push(int node) {
        stacks1.push(node);
        if(stacks2.size()==0){
            stacks2.push(node);
        }else{
            if(node>stacks2.peek()){
                stacks2.push(stacks2.peek());
            }else {
                stacks2.push(node);
            }
        }
    }
    public  void pop() {
        if(stacks1.size()>0)
        stacks1.pop();
        if(stacks2.size()>0)
        stacks2.pop();
    }

    public  int top() {
        if(stacks1.size()>0){
            return stacks1.peek();
        }
        return 0;
    }

    public  int min() {
        if(stacks2.size()>0){
            return stacks2.peek();
        }else {
            return 0;
        }
    }
}