重建二叉树

经典的题目，已知一颗树的前序遍历和中序遍历，求这个树的后序遍历。

#include <iostream>#include<stdlib.h>#include<stdio.h>using namespace std;struct TreeNode{    int key;    TreeNode* left;    TreeNode* right;};TreeNode* CreateTree(int *pre_order,int pre_l,int pre_r,int * mid_order,int mid_l,int mid_r){    if(pre_r-pre_l<0)        return NULL;    TreeNode* root;    root=new TreeNode;    root->key=pre_order[pre_l];    if(pre_l==pre_r)    {        root->left=NULL;        root->right=NULL;        return root;    }    int index;    for(index=mid_l;index<=mid_r;index++)    {        if(mid_order[index]==pre_order[pre_l])            break;    }    root->left=CreateTree(pre_order,pre_l+1,pre_l+(index-mid_l),mid_order,mid_l,index-1);    root->right=CreateTree(pre_order,pre_l+(index-mid_l)+1,pre_r,mid_order,index+1,mid_r);    return root;}void printtree(TreeNode *t){    if(t!=NULL)    {        printtree(t->left);        printtree(t->right);        cout<<t->key;    }}int main(){    int pre_order[]={1,2,4,5,3,6,7};    int mid_order[]={4,2,5,1,6,3,7};    TreeNode* root=new TreeNode;    root= CreateTree(pre_order,0,6,mid_order,0,6);    printtree(root);    return 0;}