筆試題：用二叉樹構造雙向鏈表

#include <iostream>
#include <string.h>
using namespace std;
struct Node
{
    Node *left;//相當於雙向鏈表的prev指針。
    Node *right;//相當於雙向鏈表的next指針。
    char data;
    Node(char d = char()):data(d),left(NULL),right(NULL){}
};

class MTree
{
    public:
    MTree():root(NULL){}
    void Create_Tree(char *VLR,char *LVR)
    {
        int n = strlen(LVR);
        Create_Tree(root,VLR,LVR,n);    
    }
    void Create_Tree(Node *&t,char *VLR,char *LVR,int n)
    {
        //構造二叉樹。
        if(n==0)return ;
        int i = 0;
        while(VLR[0]!=LVR[i])i++;
        t = new Node(VLR[0]);
        Create_Tree(t->left,VLR+1,LVR,i);
        Create_Tree(t->right,VLR+i+1,LVR+i+1,n-i-1);    
    }   
    void Create_DList(MTree &mt)
    {
        Node *pr = NULL;
        Create_DList(root,pr,mt.root);
    }
    static void Printf(MTree &mt)
    {//雙向鏈表打印。
       Node *p = mt.root;
       while(p!=NULL)
        {
          cout<<p->data<<" ";
          p=p->right;
                }
    }
    private:
    void Create_DList(Node *t,Node *&pr,Node *&mt)
    {
        //構造雙向鏈表。
      if(t==NULL)
            {
        return ;
        }   
        Create_DList(t->left,pr,mt);
        if(t!=NULL)
         {
        t->left=pr;
        if(pr)
        pr->right = t;
        if(pr==NULL)mt=t;
         }
        if(pr!=NULL && pr->right==NULL)
         {
               pr->right=t;
           t->left = pr;
             }
         pr = t;
         Create_DList(t->right,pr,mt);
    }

    private:
    Node *root;
};
int main()
{
    char VLR[]="ABCDEFG";
    char LVR[]="CBDAFEG";

    MTree mt;
    mt.Create_Tree(VLR,LVR);
    MTree mtlist;
    mt.Create_DList(mtlist);
    MTree :: Printf(mtlist);
    return 0;
}