BUUCTF-LeftOrRight

题目描述：
Left?Middle?No，I want right！（flag is right？！）
题目下载

给了一个打不开的图片，用notepad打开发现首位有奇怪的十六进制数，选中转换为ascii，上半部分是f09e54c1bad2x38mvyg7wzlsuhkijnop，下半部分是905e4c1fax328mdyvg7wbsuhklijznop。涉及到二叉树的遍历，题里提示左和中，就是先序和中序。
ESE师傅的脚本如下：

#include <iostream>    
#include <fstream>    
#include <string>    
#include <cstring>
using namespace std;
struct TreeNode
{
    struct TreeNode* left;
    struct TreeNode* right;
    char  elem;
};
void BinaryTreeFromOrderings(char* inorder, char* preorder, int length)
{
    if (length == 0)
    {
        //cout<<"invalid length";  
        return;
    }
    TreeNode* node = new TreeNode;//Noice that [new] should be written out.  
    node->elem = *preorder;
    int rootIndex = 0;
    for (; rootIndex < length; rootIndex++)
    {
        if (inorder[rootIndex] == *preorder)
            break;
    }
    //Left  
    BinaryTreeFromOrderings(inorder, preorder + 1, rootIndex);
    //Right  
    BinaryTreeFromOrderings(inorder + rootIndex + 1, preorder + rootIndex + 1, length - (rootIndex + 1));
    cout << node->elem;
    return;
}
int main(int argc, char* argv[])
{
    printf("You know the preorder and the middle order, can you find out the post order!\n");
    char* pr = "f09e54c1bad2x38mvyg7wzlsuhkijnop";
    char* mid = "905e4c1fax328mdyvg7wbsuhklijznop";
    int len = strlen(mid);
    BinaryTreeFromOrderings(mid, pr, len);
    printf("\n");
    return 0;
}