二叉树 前序遍历、中序遍历和后序遍历之间还原二叉树

 1 // 类定义代码
 2 struct TreeNode
 3 {
 4     char val;
 5     TreeNode* left;
 6     TreeNode* right;
 7     TreeNode(char x) : val(x), left(NULL), right(NULL) {}
 8  }; 
 9 int main()
10 {
11     char* pre = "ACDEBF";
12     char* vin = "DCEABF";
13     char* post = "DECFBA"; 
14     return 0;
15 } 

 1 TreeNode* BinaryTreeFromOrderings(char* pre, char* vin, int length)
 2  {
 3      if( length == 0 ) return NULL;
 4 
 5      int rootIndex = 0;
 6      // 寻找当前根节点，记录子树元素个数 
 7      for(; rootIndex < length; rootIndex ++)
 8          if( vin[rootIndex] == pre[0] ) break;
 9      
10     TreeNode* tree = new TreeNode( vin[rootIndex] );
11     // 返回当前左子树 
12     tree ->left = BinaryTreeFromOrderings(pre + 1, vin, rootIndex );
13     // 返回当前右子树 
14     tree ->right = BinaryTreeFromOrderings(pre + rootIndex + 1, vin + rootIndex + 1, length - (rootIndex + 1));
15     
16     return tree;
17  }

TreeNode* BinaryTreeFromPostings(char* vin, char* post, int length)
 {
     if( length == 0 ) return NULL;

     int rootIndex = 0;
     // 寻找当前根节点，记录子树元素个数 
     for(; rootIndex < length; rootIndex ++)
         if( vin[rootIndex] == post[length - 1]) break;
     
    TreeNode* tree = new TreeNode( vin[rootIndex] );
    // 返回当前右子树 
    tree ->right = BinaryTreeFromPostings(vin + rootIndex + 1, post + rootIndex, length - (rootIndex + 1) );
    // 返回当前左子树 
    tree ->left = BinaryTreeFromPostings(vin, post, rootIndex );
    
    return tree;
 }