设计一个有getMin的栈

方法一：

import java.util.Stack;
import java.util.Scanner;
public class Main{
    private Stack<Integer> numStack;
    private Stack<Integer> minStack;
    public Main(){
        numStack = new Stack<Integer>();
        minStack = new Stack<Integer>();
    }
    public void push(int num){
        if(minStack.isEmpty()){
            minStack.push(num);
        }else{
            //int min = minStack.peek();
            //min = (num < min) ? num : min;
            int min = Math.min(minStack.peek(),num);
            minStack.push(min);
        }
        numStack.push(num);
    }
    public int pop(){
        if(numStack.isEmpty()){
            throw new RuntimeException("stack is empty!");
        }
        minStack.pop();
        return numStack.pop();
    }

    public int getMin(){
        if(minStack.isEmpty()){
            throw new RuntimeException("stack is empty!");
        }
        return minStack.peek();
    }
    public static void main(String[] args){
        Main myClass = new Main();
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        scanner.nextLine();
        String[] line; 
        for(int i = 0; i < N; i++){
            line = scanner.nextLine().split(" ");
            if(line[0].equals("getMin")){
                System.out.println(myClass.getMin());
            }else if(line[0].equals("push")){
                myClass.push(Integer.valueOf(line[1]));
            }else{
                myClass.pop();
            }
        }
    }
}

方法2：

import java.util.Stack;
import java.util.Scanner;
public class Main{
    private Stack<Integer> numStack;
    private Stack<Integer> minStack;
    public Main(){
        numStack = new Stack<Integer>();
        minStack = new Stack<Integer>();
    }
    public void push(int num){
        if(minStack.isEmpty()){
            minStack.push(num);
        }else if(num <= getMin()){
            minStack.push(num);
        }
        numStack.push(num);
    }
    public int pop(){
        if(numStack.isEmpty()){
            throw new RuntimeException("stack is empty!");
        }
        int value = numStack.pop();
        if(value == getMin()){
            minStack.pop();
        }
       // if(numStack.peek() == minStack.peek()){
         //   minStack.pop();
        //}
        return value;
    }

    public int getMin(){
        if(minStack.isEmpty()){
            throw new RuntimeException("stack is empty!");
        }
        return minStack.peek();
    }
    public static void main(String[] args){
        Main myClass = new Main();
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        scanner.nextLine();
        String[] line; 
        for(int i = 0; i < N; i++){
            line = scanner.nextLine().split(" ");
            if(line[0].equals("getMin")){
                System.out.println(myClass.getMin());
            }else if(line[0].equals("push")){
                myClass.push(Integer.valueOf(line[1]));
            }else{
                myClass.pop();
            }
        }
    }
}

遇到了问题，提交几次都是失败的，后来提交又成功了，什么鬼。。