此为由二叉树前序序列和中序序列求后序序列的代码，运行错误，求大神指点错在哪里

#include<iostream>
#include<stdlib.h>
#include<stdio.h>
#include<string.h>
using namespace std;
typedef struct vode
{
    char date;
    struct vode *l,*r;
}bitree;
void getpreordertraverse(bitree *root,char pre[],char in[],int ps,int s,int n);
void postordertraverse(bitree *root);
int main()
{
    int zong ;
    cin>>zong;
    while(zong--)
    {
        char pre[100],in[100];
        cin>>pre>>in;
        int len=strlen(pre);
        bitree *root;
        getpreordertraverse(root,pre,in,0,0,len);
        postordertraverse(root);
        cout<<endl;
    }
    return 0;
}
void getpreordertraverse(bitree *root,char pre[],char in[],int ps,int s,int n)
{
      if(n==0)root=NULL;
      else
      {
          root=(bitree *)malloc(sizeof(bitree));
          root->date=pre[ps];
          int k;
          for(k=s;k<=s+n-1;k++)
              if(in[k]==pre[ps])
                  break;
          getpreordertraverse(root->l,pre,in,ps+1,s,k-s);
          getpreordertraverse(root->r,pre,in,ps+1+(k-s),k+1,n-(k-s)-1);
      }
}
void postordertraverse(bitree *root)
{
    if(root)
    {
        postordertraverse(root->l);
        postordertraverse(root->r);
        cout<<root->date;
    }
}