数据结构与算法-第12章二叉树和其他树-002克隆二叉树

例子中二叉树用链表示

1.后序遍历克隆和前序遍历克隆

package chapter12Tree;

//In writing the cloning codes, we assume that we are not to 
//make clones of the elements in the nodes. Only the tree structure is to be cloned. 
//In case the elements are also to be cloned, then we must replace all occurrences 
//of element by code to first cast element into a CloneableObject, 
//and then invoke the method clone on the reulting object.
public class BinaryTreeCloning
{
   /** preorder cloning
     * @return root of clone */
   public static BinaryTreeNode preOrderClone(BinaryTreeNode t)
   {
      if (t != null)
      {// nonempty tree
         // make a clone of the root
         BinaryTreeNode ct = new BinaryTreeNode(t.element);

         // now do the subtrees
         ct.leftChild = preOrderClone(t.leftChild);    // clone left subtree
         ct.rightChild = preOrderClone(t.rightChild);  // clone right subtree
         return ct;
      }
      else
         return null;
   }

   /** postorder cloning
     * @return root of clone */
   public static BinaryTreeNode postOrderClone(BinaryTreeNode t)
   {
      if (t != null)
      {// nonempty tree
         // clone left subtree
         BinaryTreeNode cLeft = postOrderClone(t.leftChild);

         // clone right subtree
         BinaryTreeNode cRight = postOrderClone(t.rightChild);

         // clone root
         return new BinaryTreeNode(t.element, cLeft, cRight);
      }
      else
         return null;
   }
}

class BinaryTreeNode {
    int element;
    BinaryTreeNode leftChild, rightChild;
    
    // constructors
    BinaryTreeNode() {}
    
    BinaryTreeNode(int element) {
        this.element = element;
        this.rightChild = null;
        this.leftChild = null;
    }
    BinaryTreeNode(int element, BinaryTreeNode rc, BinaryTreeNode lc) {
        this.element = element;
        this.rightChild = rc;
        this.leftChild = lc;
    }    
}

The recursion stack space needed by both the preorder and postorder copy methods is O(h), where h is the height of the binary tree being cloned