已知前序中序遍历，求树的后续遍历

#define M 100
struct BTN
{
  int value;
  struct BTN* left;
  struct BTN *right;
};
int pre[8]={1,2,4,7,3,5,6,8};
int mid[8]={4,7,2,1,5,3,8,6};
int n=8;

struct BTN *rebuild(int k,int l,int r)
{
  if(k>=n||l>r)
    return NULL;
  struct BTN *root=new struct BTN;
  root->value=pre[k];
  root->left=root->right=NULL;
  for(int i=l;i<=r;i++)
  {
    if(mid[i]==pre[k])
    {
      root->left=rebuild(k+1,l,i-1);
      root->right=rebuild(k+1+i-l,i+1,r);
      return root;
    }
  }
}

struct BTN *rebuild_after(int n)
{

  return rebuild(0,0,n-1);
}

void after_print(struct BTN *root)
{
  if(root==NULL)
    return ;
  after_print(root->left);
  after_print(root->right);
  printf("%d ",root->value);
}


int main()
{
  string s;
  n=8;
  struct BTN *root=rebuild_after(n);
  after_print(root);
}