扩展二叉树建立（#表示空节点）

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct Node{
   int val;
   struct Node* left;
   struct Node* right;
}Node;

Node* createTree(char *s);
void preOrder(Node *root);
int main(){
  //空节点用#表示的序列
  char s[15]="123###4#5##";
  Node* tree=createTree(s);
  preOrder(tree);


    return 0;
}

int where=0;//字符串消费到哪个位置了

Node* createTree(char *s){
   //s为前序序列
   Node *root;
   if(where==strlen(s)){
       return NULL;
    }
   char ch=s[where];
    
   if(ch=='#'){
      where++;
      return NULL;
   }else{
      root=(Node *)malloc(sizeof(Node));
      root->val=s[where++]-'0';
      root->left=createTree(s);
      root->right=createTree(s);
   }
   return root;
}
void preOrder(Node *root){
   if(root==NULL){
      return ;
   }
   printf("%d ",root->val);
   preOrder(root->left);
   preOrder(root->right);
}