//重建二叉樹：輸入某二叉樹的前序和中序遍歷，重建出該二叉樹
#include<stdio.h>
#include<malloc.h>

typedef struct binarytreenode
{
  int value;
  struct  binarytreenode *left;
  struct  binarytreenode *right;
}binary;


binary* constructcore(int *startpreorder,int *endpreorder,int *startinorder,int *endinorder)
{
  int *rootinorder=NULL;
  int leftlength =0;                     //左子樹的長度
  int * leftpreend =NULL;                //前序遍歷中左子樹的終結點
  int rootvalue=startpreorder[0];        //前序遍歷中的第一個結點的值便是根節點的值

  binary *root = malloc(sizeof(binary));
  root->value=rootvalue;
  root->left=root->right=NULL;

  if(startpreorder==endpreorder)
  {
     if(startinorder==endinorder&& *startpreorder==*startinorder)    //前序遍歷和中序遍歷中都只有根節點的情況
		 return root;
	 else
		 printf("invalid input\n");
	    // return root;
  }
 
 //在中序遍歷中找到根節點的值
  rootinorder = startinorder;
  while(rootinorder<=endinorder&& *rootinorder != rootvalue)
  {
    ++rootinorder;
  }

  if(rootinorder==endinorder&& *rootinorder != rootvalue)
      printf("invalid input");

  leftlength = rootinorder-startinorder;   
  leftpreend = startpreorder + leftlength;  
  if(leftlength>0)
  {
    root->left = constructcore(startpreorder+1,leftpreend,startinorder,rootinorder-1);  //構建左子樹
  }
  if(leftlength < endpreorder-startpreorder)
  {
    root->right = constructcore(leftpreend+1,endpreorder,rootinorder+1,endinorder);
  }

  return root;
  
}



binary *construct(int *preorder,int *inorder,int length)
{
   if(preorder==NULL||inorder==NULL||length<=0)
	   return NULL;
   else
	   return constructcore(preorder,preorder+length-1,inorder,inorder+length-1);
}


int main()
{
	int preorder[]={1,2,4,7,3,5,6,8};
	int inorder[]={4,7,2,9,5,3,8,6};
	binary *root;
	root=construct(preorder,inorder,8);
    printf("%d\n",root->value);
	return 0;
}