二、栈与队列

栈的构造：

import java.util.Arrays;
/**
 * @author zhou
 * @date 2021-5-7 8:12
 */
public class MyStack {
    private int[] elements;
    public MyStack(){
        elements = new int[0];
    }

    public void show(){ // 打印 栈
        System.out.println(Arrays.toString(elements));
    }

    public void push(int element) { // 入栈
        int[] newArr = new int[elements.length + 1];
        for (int i = 0; i < elements.length; i++) {
            newArr[i] = elements[i];
        }
        newArr[elements.length] = element;
        elements = newArr;
    }

    public int pop(){ // 出栈
        if (elements.length == 0) {
            throw new ArrayIndexOutOfBoundsException("Stack is empty");
        }
        // 取出数组最后一个元素
        int element=elements[elements.length - 1];
        int[] newArr = new int[elements.length - 1];
        for (int i = 0; i < newArr.length; i++) {
            newArr[i] = elements[i];
        }
        elements = newArr;
        return element;
    }

    public int peek(){ // 显示栈的顶端元素
        if (elements.length == 0) {
            throw new ArrayIndexOutOfBoundsException("Stack is empty");
        }
        return elements[elements.length - 1];
    }

    public boolean isEmpty(){ // 判断栈是否为空
        return elements.length == 0;
    }

}

栈的测试类：

/**
 * @author zhou
 * @date 2021-5-7
 * 测试类  测试MyStack 栈
 */

public class TestMyStack {
    public static void main(String[] args) {
        MyStack ms = new MyStack();
        ms.push(11);
        ms.push(22);
        ms.push(33);
        ms.push(16);
        ms.show();
        int pop = ms.pop();
        System.out.println(pop);
        ms.show();
        System.out.println(ms.isEmpty());
        System.out.println(ms.peek());

    }
}

运行结果：

[11, 22, 33, 16]
16
[11, 22, 33]
false
33

队列的构造：

import java.util.Arrays;

/**
 * @author zhou
 * @date 2021-5-7 14:35
 * 队列
 */
public class MyQueue {
    int[] elements;
    public MyQueue(){ // 初始化数组为0
        elements = new int[0];
    }

    public void show(){
        System.out.println(Arrays.toString(elements));

    }

    public void add(int element){ // 入队
        int[] newArr = new int[elements.length + 1];
        for (int i = 0; i < elements.length; i++) {
            newArr[i] = elements[i];
        }
        newArr[elements.length] = element;
        elements = newArr;
    }

    public void poll() { // 出队
        if (elements.length == 0) {
            throw new ArrayIndexOutOfBoundsException("Queue is empty");
        }
        int[] newArr = new int[elements.length - 1];
        for (int i = 0; i < newArr.length; i++) {
            newArr[i] = elements[i + 1];
        }
        elements = newArr;
    }

    public int peek() { // 查看队头元素
        if (elements.length == 0) {
            return -1;
        }
        return elements[0];
    }

    public boolean isEmpty(){
        return elements.length == 0;
    }
}

队列的测试类：

/**
 * @author zhou
 * @date 2021-5-7 14:38
 * 用于测试手写队列
 */
public class TestQueue {
    public static void main(String[] args) {
        MyQueue mq = new MyQueue();
        mq.add(22);
        mq.add(5);
        mq.add(66);
        mq.add(12);
        mq.add(33);
        mq.show();
        mq.poll(); // 出队
        mq.show();
        System.out.println(mq.isEmpty());
        System.out.println(mq.peek());

    }
}

运行结果：

[22, 5, 66, 12, 33]
[5, 66, 12, 33]
false
5