二叉树的递归遍历，用先序和中序输出后序

Little Valentine liked playing with binary trees very much. Her favorite game was constructing randomly looking binary trees with capital letters in the nodes.

This is an example of one of her creations:

                                    D
                                   / 
                                  /   
                                 B     E
                                /      
                               /         
                              A     C     G
                                         /
                                        /
                                       F

To record her trees for future generations, she wrote down two strings for each tree: a preorder traversal (root, left subtree, right subtree) and an inorder traversal (left subtree, root, right subtree).

For the tree drawn above the preorder traversal is DBACEGF and the inorder traversal is ABCDEFG.

She thought that such a pair of strings would give enough information to reconstruct the tree later (but she never tried it).

Now, years later, looking again at the strings, she realized that reconstructing the trees was indeed possible, but only because she never had used the same letter twice in the same tree.

However, doing the reconstruction by hand, soon turned out to be tedious.

So now she asks you to write a program that does the job for her!

Input Specification 

Input is terminated by end of file.

Output Specification 

Sample Input 

DBACEGF ABCDEFG
BCAD CBAD

Sample Output 

ACBFGED
CDAB



题意：给你一个二叉树的先序和中序，输出它的后序。

解题思路：因为先序的第一个就是这个二叉树的根。通过先序找到根，然后再在中序上找到根，然后从这分开，再找左边的子树的根，接下来都是这样，也就是递归了，右边也是这样。然后再递归的输出。

（参考了别人的代码，自己还是有点地方不懂，如果看不懂的话，复制这个链接，看看我参考的代码。）

http://www.cnblogs.com/zsyacm666666/p/4662576.html

（我的注释，也不一定是对的。╮(╯▽╰)╭，   我是小白，求谅解。   最好是自己把例子带入代码，模拟一遍）

 1 #include "iostream"
 2 #include "string.h"
 3 using namespace std;
 4 struct node
 5 {
 6     char dian;   //根（节点）
 7     struct node *lchild;  //左孩子
 8     struct node *rchild;  // 右孩子
 9 };
10 struct node *build(char *pre,char *in,int len)
11 {
12     struct node *p;   //一个node型的指针
13     char *q;          //字符指针
14     p=new (struct node);   //分配一个大小为node的空间给p
15     int k=0;          
16     if(len==0) return NULL;   //判断到底没有
17     p->dian=*pre;   //将先序的第一个值给dian
18     //cout<<*pre<<endl;  
19     for(q=in; q<in+len; q++)   //这里通过首地址循环。
20     {
21         if(*q==*pre) break;   //如果中序的值等于根
22         k++;        //记录循环了几次，也是记住位置
23     }
24     p->lchild=build(pre+1,in,k);    //左边递归，
25     p->rchild=build(pre+1+k,q+1,len-k-1); //右边递归
26     return p;
27 }
28 void post(struct node*p)
29 {
30     if(p!=NULL)
31     {
32         post(p->lchild);
33         post(p->rchild);
34         cout<<p->dian;
35     }
36 }
37 int main()
38 {
39     char a[100],b[100];
40     while(cin>>a>>b)
41     {
42         struct node*root;
43         root=build(a,b,strlen(a));
44         post(root);
45         cout<<endl;
46     }
47     return 0;
48 }