從這個月開始得準備春招的東西，所以打算重新學習資料結構與演算法，以後的部落格就以這個為主。

　　今天是線性結構中的雙向連結串列。

　　程式碼實現與測試：

　　DoubleLinkNode：　

package linear.doublelink;

/**
 * @Description: 連結串列節點結構體
 * @Auther: Weijie.Zhang
 * @Date: 2018/11/1 17:03
 */
public class DoubleLinkNode<T> {
    public T value;
    public DoubleLinkNode pre;
    public DoubleLinkNode next;

    public DoubleLinkNode(T value) {
        this.value = value;
    }

    public DoubleLinkNode(T value, DoubleLinkNode pre, DoubleLinkNode next) {
        this.value = value;
        this.pre = pre;
        this.next = next;
    }
}

DoubleLink：

package linear.doublelink;

/**
 * @Description: 連結串列實現
 * @Auther: Weijie.Zhang
 * @Date: 2018/11/1 17:04
 */
public class DoubleLink<T> {
    //表頭
    private DoubleLinkNode<T> head;
    //節點個數
    private int count;

    public DoubleLink() {
        head = new DoubleLinkNode<T>(null, null, null);
        head.pre = head.next = head;
        count = 0;
    }

    //返回節點個數
    public int size() {
        return count;
    }

    //返回連結串列是否為空
    public Boolean isEmpty() {
        if (count == 0) {
            return true;
        } else {
            return false;
        }
    }

    //獲取第index位置上的節點
    public DoubleLinkNode<T> get(int index) {
        if (index < 0 || index >= count) {
            System.out.println("索引超出範圍");
            throw new IndexOutOfBoundsException();
        }

        //正向查詢
        if (index <= count / 2) {
            DoubleLinkNode doubleLinkNode = head.next;
            for (int i = 0; i < index; i++)
                doubleLinkNode = doubleLinkNode.next;
            return doubleLinkNode;
        }

        //反向查詢
        DoubleLinkNode doubleLinkNode = head.pre;
        int pos = count - index - 1;
        for (int i = 0; i < pos; i++)
            doubleLinkNode = doubleLinkNode.pre;
        return doubleLinkNode;
    }

    //獲取第一個節點的值
    public T getFirstValue() {
        return get(0).value;
    }

    //獲取最後一個節點的值
    public T getLastValue() {
        return get(count - 1).value;
    }

    //獲取第index節點的值
    public T getIndexValue(int index) {
        return get(index).value;
    }

    //將節點插入到index位置
    public void insert(int index, DoubleLinkNode<T> doubleLinkNode) {
        if (index < 0 || index > count) {
            System.out.println("超出索引範圍");
            throw new IndexOutOfBoundsException();
        }

        if (index == 0) {
            head.next.pre = doubleLinkNode;
            head.next = doubleLinkNode;
            count++;
            return;
        }

        if (index == count) {
            doubleLinkNode.next = head;
            doubleLinkNode.pre = head.pre;
            head.pre.next = doubleLinkNode;
            head.pre = doubleLinkNode;
            count++;
            return;
        }

        for (int i = 0; i < index; i++) {
            DoubleLinkNode linkNode = get(index);
            doubleLinkNode.pre = linkNode.pre;
            doubleLinkNode.next = linkNode;
            linkNode.pre.next = doubleLinkNode;
            linkNode.pre = doubleLinkNode;
            count++;
            return;
        }
    }

    //刪除index上的節點
    public void delete(int index) {
        DoubleLinkNode doubleLinkNode = get(index);
        doubleLinkNode.pre.next = doubleLinkNode.next;
        doubleLinkNode.next.pre = doubleLinkNode.pre;
        count--;
        return;
    }

    //修改index節點上的值
    public void change(int index, T value) {
        get(index).value = value;
        return;
    }
}

MainTest：

package linear.doublelink;

/**
 * @Description: 測試
 * @Auther: Weijie.Zhang
 * @Date: 2018/11/1 17:57
 */
public class MainTest {
    public static void main(String[] args) {
        DoubleLink<Integer> doubleLink = new DoubleLink<>();
        int i;
        for (i = 0; i < 10; i++) {
            DoubleLinkNode<Integer> doubleLinkNode = new DoubleLinkNode<>(i + 22);
            doubleLink.insert(i, doubleLinkNode);
        }
        System.out.println(doubleLink.getFirstValue());
        System.out.println(doubleLink.getLastValue());
        System.out.println(doubleLink.getIndexValue(7));

        doubleLink.delete(4);
        doubleLink.insert(9,new DoubleLinkNode<Integer>(10));

        for (int j = 0; j < doubleLink.size(); j++) {
            System.out.print(doubleLink.get(j).value + "    ");
        }
    }
}