微软面试100题系列---把二叉查找树转换成排序的双向链表

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题目：把二叉查找树转换成排序的双向链表

输入：一个二叉查找树

输出：排序的双向链表；

要求：不能创建任何新的节点，只能调整指针的方向；

实现

思路：对二叉查找树进行中序遍历，对遍历的当前节点加入到链表末尾即可；加入链表的head和tail，当前的节点curr:

curr->next=null;curr->pre=tail;tail->next=curr;tail=curr;

实现代码：

public class Num1 {    public static BSTreeNode head=null;    public static BSTreeNode tail=null;    /*     * insert search tree to double link     */    public static void main(String[] args) {        //create a search tree to test        BSTreeNode root=null;        root=addBSTreeNode(root,10);        addBSTreeNode(root,6);        addBSTreeNode(root,14);        addBSTreeNode(root,4);        addBSTreeNode(root,8);        addBSTreeNode(root,12);        addBSTreeNode(root,16);        inOrderBSTree(root);        //print result        BSTreeNode node=head;        while(node.right!=null){            System.out.print(node.value+" ");            node=node.right;        }    }    public static BSTreeNode addBSTreeNode(BSTreeNode root,int value){        BSTreeNode node=new BSTreeNode(value,null,null);        if(root==null){            root=node;            return root;        }        BSTreeNode curr=root;        BSTreeNode parent=null;        while(curr!=null){            parent=curr;            if(curr.value<value){                curr=curr.right;            }else{                curr=curr.left;            }        }        //insert node to parent's child        if(parent.value<value){            parent.right=node;        }else{            parent.left=node;        }        return root;    }    public static void inOrderBSTree(BSTreeNode root){        if(root==null){            return;        }        if(root.left!=null){            inOrderBSTree(root.left);        }        //System.out.println(root.value);        convertIntoDoubleList(root);        if(root.right!=null){            inOrderBSTree(root.right);        }    }    private static void convertIntoDoubleList(BSTreeNode node) {        node.left=tail;        if(tail==null){            head=node;        }else{            tail.right=node;        }        tail=node;          }}class BSTreeNode{     int value;     BSTreeNode left;     BSTreeNode right;    public BSTreeNode(int value,BSTreeNode left,BSTreeNode right){        this.value=value;        this.left=left;        this.right=right;    }    public BSTreeNode(int value){        this(value,null,null);    }}

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