玩轉數據結構<三> 線性數據結構

鏈表

• 代碼定義鏈表

public class LinkedList<E> {

    //對外屏蔽內部複雜的實現機制
    private  class Node{

        public E e;
        public Node next;

        public Node(E e,Node next){
            this.e = e;
            this.next = next;
        }

        public Node(E e){
            this(e,null);
        }

        public Node(){
            this(null,null);
        }

        @Override
        public String toString(){
            return e.toString();
        }
    }

    private Node dummyHead;
    private int size;

    public LinkedList(){
        dummyHead = new Node(null,null);
        size = 0;
    }

    //獲取鏈表中的元素個數
    public int getSize(){
        return size;
    }

    //返回鏈表是否爲空
    public boolean isEmpty(){
        return size == 0;
    }



    // 在鏈表的index(0-based)位置添加新的元素e

    public void add(int index,E e){

        if(index < 0 || index > size){
            throw new IllegalArgumentException("Add failed. Illegal index.");
        }

            Node prev = dummyHead;
            for(int i = 0;i < index ; i++){
                prev = prev.next;
            }

            prev.next = new Node(e,prev.next);
        }
    // 在鏈表頭添加新的元素e
    public void addFirst(E e){
     /* Node node = new Node(e);
        node.next = head;
        head = node;*/
        add(0,e);
        size ++;
    }

    //在鏈表末尾添加新的元素e
    public void addLast(E e){
        add(size,e);
    }

    // 得到鏈表的第index(0-based)個位置的元素
    // 在鏈表中不是一個經常使用的操做,練習用：)
    public E get(int index){
        if(index < 0 || index >= size){
            throw new IllegalArgumentException("Get failed. Illegal index.");
        }
            Node cur = dummyHead.next;
            for(int i = 0;i < index; i++){
                cur = cur.next;
            }
            return cur.e;
    }

    //獲取鏈表的第一個元素
    public E getFirst() {
        return get(0);
    }

    //得到鏈表的最後一個元素
    public E getLast(){
        return get(size - 1);
    }

    //修改鏈表的第index(0-based)個位置的元素爲e
    //在鏈表中不是一個經常使用的操做,練習用：)
    public void ser(int index,E e){
        if(index < 0 || index >= size){
            throw new IllegalArgumentException("Ser fauked.Illegal index.");
        }
        Node cur = dummyHead.next;
        for(int i = 0; i < index; i++){
            cur = cur.next;
        }
        cur.e = e;
    }

    //查找鏈表中是否有元素e
    public boolean contains(E e){
        Node cur = dummyHead.next;
        while (cur != null){
            if(cur.e.equals(e)){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    //從鏈表中刪除index(0-bassed)位置的元素，返回刪除的元素
    //在鏈表中不是一個經常使用的操做，練習用：）
    public E remove(int index){
        if(index < 0 || index >= size){
            throw new IllegalArgumentException("Remove failed. Index is illegal");
        }
        Node prev = dummyHead;
        for(int i = 0;i < index ; i ++){
            prev = prev.next;
        }

        Node retNode = prev.next;
        prev.next = retNode.next;
        retNode.next = null;
        size --;
        return retNode.e;
    }
    // 從鏈表中刪除第一個元素,返回刪除的元素
    public E removeFirst(){
        return remove(0);
    }

    // 從鏈表中刪除最後一個元素,返回刪除的元素
    public E removeLast(){
        return remove(size - 1);
    }

    @Override
    public String toString(){

        StringBuilder res = new StringBuilder();
        Node cur = dummyHead.next;
        while (cur != null){
            res.append(cur + "->");
            cur = cur.next;
        }
//       for(Node cur = dummyHead.next;cur != null;cur = cur.next){
//           res.append(cur + "->");
//       }
        res.append("NULL");
        return res.toString();
    }

}

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• 程序主函數實現

LinkedList<Integer> linkedList = new LinkedList<>();
        for(int i = 0 ;i < 5 ;i ++){
        linkedList.addFirst(i);
        System.out.println(linkedList);
    }
        linkedList.add(2,666);
        System.out.println(linkedList);
        linkedList.remove(2);
        System.out.println(linkedList);
        linkedList.removeFirst();
        System.out.println(linkedList);
        linkedList.removeLast();
        System.out.println(linkedList);

}
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使用鏈表實現棧

• 使用鏈表實現棧結構

public class LinkedListStack<E> implements Stack<E> {

    private LinkedList<E> list;

    public LinkedListStack(){
        list = new LinkedList<>();
    }

    @Override
    public int getSize() {
        return  0;
    }

    @Override
    public boolean isEmpty() {
        return list.isEmpty();
    }

    @Override
    public void push(E e) {
        list.addFirst(e);
    }

    @Override
    public E pop() {
        return list.removeFirst();
    }

    @Override
    public E peek() {
        return list.getFirst();
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append("Stack: top ");
        res.append(list);
        return res.toString();
    }

    public static void main(String[] args) {

        LinkedListStack<Integer> stack = new LinkedListStack<>();
        for(int i = 0 ;i < 5 ;i ++){
            stack.push(i);
            System.out.println(stack);
        }
        stack.pop();
        System.out.println(stack);

    }

}

複製代碼

• 性能測試代碼

//方法
 private static double testStack(Stack<Integer> stack, int opCount){
        long startTime = System.nanoTime();
        Random random = new Random();
        for(int i = 0 ;i < opCount; i++){
            stack.push(random.nextInt(Integer.MAX_VALUE));
        }

        for(int i = 0 ;i < opCount; i++) {
            stack.pop();
        }

        long endTime = System.nanoTime();
        return(endTime - startTime) / 1000000000.0;

    }
//主函數：
  int opCount = 100000;
 ArrayStack<Integer> arrayStack = new ArrayStack<>();
        double time1 = testStack(arrayStack,opCount);
        System.out.println("ArrayQueue,time: "+ time1 +"s");
        LinkedListStack<Integer> linkedListStack = new LinkedListStack<>();
        double time2 = testStack(linkedListStack,opCount);
        System.out.println("LoopQueue,time: "+ time2 +"s");
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使用鏈表實現隊列

• 因爲沒有dummyHead,要注意鏈表爲空的狀況

public class LinkedListQueue<E> implements Queue<E> {

    private class Node {

    public E e;
    public Node next;

    public Node(E e, Node next) {
        this.e = e;
        this.next = next;
    }

    public Node(E e) {
        this(e, null);
    }

    public Node() {
        this(null, null);
    }

    @Override
    public String toString(){ return e.toString();}



}

    private Node head,tail;
    private int size;

    public LinkedListQueue(){
        head = null;
        tail = null;
        size = 0;
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return size == 0;
    }

    @Override
    public void enqueue(E e) {
        if(tail == null){
            tail = new Node(e);
            head = tail;
        }else{
            tail.next = new Node(e);
            tail = tail.next;
        }
        size ++;
    }

    @Override
    public E dequeue() {
        if(isEmpty()){
            throw new IllegalArgumentException("Cannot dequeque from an empty queue");
        }
        Node retNode = head;
        head = head.next;
        retNode.next = null;
        if(head == null){
            tail = null;
        }
        size --;
        return retNode.e;
    }

    @Override
    public E getFront() {
        if(isEmpty()){
            throw new IllegalArgumentException("Queue is empty.");
        }
        return head.e;
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append("Queue: front ");

        Node cur = head;
        while (cur != null){
            res.append(cur + "->");
            cur = cur.next;
        }
        res.append("Null tail");
        return  res.toString();
    }

    public static void main(String[] args){
        LinkedListQueue<Integer> queue = new LinkedListQueue<>();
        for(int i = 0 ; i < 10 ; i++){
            queue.enqueue(i);
            System.out.println(queue);
            if(i % 3 == 2){
                queue.dequeue();
                System.out.println(queue);
            }
        }

    }
}

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