实现一个特殊的栈，在实现栈的基本功能的基础上,再实现返 回栈中[最小元素]的操作。

package basic_class_03;

import java.util.Stack;

/**
 * 实现一个特殊的栈，在实现栈的基本功能的基础上，
 * 再实现返 回栈中[最小元素]的操作。 
 * 
 * 下面的两种实现方法几乎是一样的
 * 
 * @author lenovo
 *
 */
public class Code_02_GetMinStack {


    public static class MyStack1 {
        private Stack<Integer> stackData;   // 用来存放数据的栈
        private Stack<Integer> stackMin;

        public MyStack1() {
            this.stackData = new Stack<Integer>();
            this.stackMin = new Stack<Integer>();
        }


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


        public int pop() {
            if(this.stackData.isEmpty()) {
                throw new RuntimeException("Your stack is empty");
            }
            int value = this.stackData.pop();
            if(value == this.getmin()) {
                this.stackMin.pop();
            }
            return value;
        }


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


    }

    public static void main(String[] args) {
        MyStack1 stack1 = new MyStack1();
        stack1.push(3);
        System.out.println(stack1.getmin());
        stack1.push(4);
        System.out.println(stack1.getmin());
        stack1.push(1);
        System.out.println(stack1.getmin());
        System.out.println(stack1.pop());
        System.out.println(stack1.getmin());  
        System.out.println(stack1.pop());
        System.out.println(stack1.getmin());

        System.out.println("=============");

        /*MyStack1 stack2 = new MyStack1();
        stack2.push(3);
        System.out.println(stack2.getmin());
        stack2.push(4);
        System.out.println(stack2.getmin());
        stack2.push(1);
        System.out.println(stack2.getmin());
        System.out.println(stack2.pop());
        System.out.println(stack2.getmin());*/
    }



    public static class MyStack2 {
        private Stack<Integer> stackData;
        private Stack<Integer> stackMin;
        public MyStack2() {
            this.stackData = new Stack<Integer>();
            this.stackMin = new Stack<Integer>();
        }


        public void push(int newNum) {
            if(this.stackMin.isEmpty()) {
                this.stackMin.push(newNum);
            } else if(newNum < this.getmin()) {
                this.stackMin.push(newNum);
            } else {
                int newMin = this.stackMin.peek();
                this.stackMin.push(newNum);
            }
            this.stackData.push(newNum);
        }


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


    }



}