《程序员代码面试指南》第二章 链表问题 搜索二叉树转换为双向链表

样例

树的中序遍历：1 2 3 4 5 6 7 ，转换后双向链表的遍历：1 2 3 4 5 6 7

java代码

/**
 * @Description:搜索二叉树转换为双向链表
 * @Author: lizhouwei
 * @CreateDate: 2018/4/7 10:45
 * @Modify by:
 * @ModifyDate:
 */
public class Chapter2_15 {
    public DoubleNode treeToDubleNode(Tree tree) {
        //用队列存放将树的中序遍历
        Queue<Tree> trees = new LinkedList<Tree>();
        //中序遍历
        recInOrder(tree, trees);
        //构造双向链表
        tree = trees.poll();
        DoubleNode head = new DoubleNode(tree.vlaue);
        DoubleNode pre = head;
        DoubleNode cur = null;
        while (!trees.isEmpty()) {
            tree = trees.poll();
            cur = new DoubleNode(tree.vlaue);
            pre.next = cur;
            cur.pre = pre;
            pre = cur;
        }
        return head;
    }

    public void recInOrder(Tree tree, Queue<Tree> trees) {
        if (tree == null) {
            return;
        }
        recInOrder(tree.left, trees);
        trees.offer(tree);
        recInOrder(tree.right, trees);
    }

    //打印树
    public void recInOrder(Tree tree) {
        if (tree == null) {
            return;
        }
        recInOrder(tree.left);
        System.out.print(tree.vlaue + " ");
        recInOrder(tree.right);
    }

    //测试
    public static void main(String[] args) {
        Chapter2_15 chapter = new Chapter2_15();
        Tree root = new Tree(4);
        root.left = new Tree(2);
        root.right = new Tree(6);
        root.left.left = new Tree(1);
        root.left.right = new Tree(3);
        root.right.left = new Tree(5);
        root.right.right = new Tree(7);
        chapter.recInOrder(root);
        DoubleNode head = chapter.treeToDubleNode(root);
        Link.printDLink(head);
    }
}

class Tree {
    public int vlaue;
    public Tree left;
    public Tree right;

    public Tree(int vlaue) {
        this.vlaue = vlaue;
    }

}