acm ----树 ----problem 1

数据结构：  二叉树

运用递归的方法构造二叉树，二叉树的根节点root代表一棵二叉树。

 

#include <cstdlib>
#include <iostream>
/*
  Name:          Binary Tree template 
  Copyright: 
  Author: 
  Date: 28-04-10 11:26
  Description:     construct a binary tree
*/

using namespace std;
/**tree structure*/
struct TreeNode
{
       int val;  //data area 
       TreeNode *left, *right;  //point area
};
/**insert a val to a tree, return the root of the tree*/
TreeNode *InsertTree(TreeNode *root, int val )
{
         TreeNode *newNode;
         if(root==NULL)   //border value 
         {
                       newNode=new TreeNode;
                       newNode->val=val;
                       newNode->left=NULL;
                       newNode->right=NULL;
                       return newNode;
         }
         if(val<=root->val)
         {
                       root->left=InsertTree(root->left,val);
         }
         else
         {
                       root->right=InsertTree(root->right,val);
         }
         
         return root;
}
/**linear time*/
void DelTree(TreeNode *root)
{
     if(root->left!=NULL) DelTree(root->left);
     if(root->right!=NULL) DelTree(root->right);
     delete root;
}
/**depth-first traversal*/
void printTree(TreeNode *root, char offset[])
{
     char str[81];
     printf("%s%d\n",offset,root->val);
     sprintf(str,"%s%s",offset," ");   //write format data to string
     
     if(root->left!=NULL)
         printTree(root->left,str);
     else
         printf("%s$\n",str);
     
     if(root->right!=NULL)
         printTree(root->right,str);
     else
         printf("%s$\n",str);
     
}

int main(int argc, char *argv[])
{
    FILE *fin;
    TreeNode *root;
    int val;
    char inFile[30], str[81];
      
    scanf("%s",inFile);
    fin=fopen(inFile,"r");  //open file in current directory
    
    root=NULL;
    while(fscanf(fin,"%d",&val)!=EOF)   //scan all elem in the file
    {
          root=InsertTree(root,val);
    }
    fclose(fin);
    
    sprintf(str,"%s","");
    printTree(root,str);
    DelTree(root);
    system("PAUSE");
    return EXIT_SUCCESS;
}

递归方法理解的还不够深刻。下一次从递归开始训练