包含min函数的栈

题目描述
定义栈的数据结构，请在该类型中实现一个能够得到栈最小元素的min函数。

import java.util.Stack;

public class Solution {

    private Stack<Integer> stackData;
    private Stack<Integer> stackMin;

    public Solution(){
        stackData = new Stack<Integer>();
        stackMin = new Stack<Integer>();
    }

    public void push(int node) {
        if(stackMin.isEmpty()){
           stackMin.push(node);
        }else{
            if(node <= this.min()){
                 stackMin.push(node);
            }
        }
        stackData.push(node);
    }

    public void pop() {
        if(stackData.isEmpty()){
         //   throws new RuntimeException("Your stack is empty");
        }
        int value = this.stackData.pop();
        if(value == this.min()){
            stackMin.pop();
        }
    }

    public int top() {
        if(stackMin.isEmpty()){
            throw new RuntimeException("Your stack is empty.");
        }
        return stackMin.peek();
    }

    public int min() { 
        if(stackMin.isEmpty()){
            throw new RuntimeException("Your stack is empty.");
        }
        return stackMin.peek();
    }
}