JAVA的树形操作

      二叉树是每个节点最多有两个子树的有序树。通常子树被称作“左子树”（left subtree）和“右子树”（right subtree）。二叉树常被用于实现二叉查找树和二叉堆。在JAVA中可以用类很方便的实现二叉树：

      

package MyTree;

//tree.java
//demonstrates binary tree
//to run this program: C>java TreeApp
import java.io.*;
import java.util.*;               // for Stack class
////////////////////////////////////////////////////////////////
class Node
{
public int iData;              // data item (key)
public double dData;           // data item
public Node leftChild;         // this node's left child
public Node rightChild;        // this node's right child

public void displayNode()      // display ourself
   {
   System.out.print('{');
   System.out.print(iData);
   System.out.print(", ");
   System.out.print(dData);
   System.out.print("} ");
   }
}  // end class Node
////////////////////////////////////////////////////////////////
class Tree
{
private Node root;             // first node of tree

//-------------------------------------------------------------
public Tree()                  // constructor
   { root = null; }            // no nodes in tree yet
//-------------------------------------------------------------
public Node find(int key)      // find node with given key
   {                           // (assumes non-empty tree)
   Node current = root;               // start at root
   while(current.iData != key)        // while no match,
      {
      if(key < current.iData)         // go left?
         current = current.leftChild;
      else                            // or go right?
         current = current.rightChild;
      if(current == null)             // if no child,
         return null;                 // didn't find it
      }
   return current;                    // found it
   }  // end find()
//-------------------------------------------------------------
public void insert(int id, double dd)
   {
   Node newNode = new Node();    // make new node
   newNode.iData = id;           // insert data
   newNode.dData = dd;
   if(root==null)                // no node in root
      root = newNode;
   else                          // root occupied
      {
      Node current = root;       // start at root
      Node parent;
      while(true)                // (exits internally)
         {
         parent = current;
         if(id < current.iData)  // go left?
            {
            current = current.leftChild;
            if(current == null)  // if end of the line,
               {                 // insert on left
               parent.leftChild = newNode;
               return;
               }
            }  // end if go left
         else                    // or go right?
            {
            current = current.rightChild;
            if(current == null)  // if end of the line
               {                 // insert on right
               parent.rightChild = newNode;
               return;
               }
            }  // end else go right
         }  // end while
      }  // end else not root
   }  // end insert()
//-------------------------------------------------------------
public boolean delete(int key) // delete node with given key
   {                           // (assumes non-empty list)
   Node current = root;
   Node parent = root;
   boolean isLeftChild = true;

   while(current.iData != key)        // search for node
      {
      parent = current;
      if(key < current.iData)         // go left?
         {
         isLeftChild = true;
         current = current.leftChild;
         }
      else                            // or go right?
         {
         isLeftChild = false;
         current = current.rightChild;
         }
      if(current == null)             // end of the line,
         return false;                // didn't find it
      }  // end while
   // found node to delete

   // if no children, simply delete it
   if(current.leftChild==null &&
                                current.rightChild==null)
      {
      if(current == root)             // if root,
         root = null;                 // tree is empty
      else if(isLeftChild)
         parent.leftChild = null;     // disconnect
      else                            // from parent
         parent.rightChild = null;
      }

   // if no right child, replace with left subtree
   else if(current.rightChild==null)
      if(current == root)
         root = current.leftChild;
      else if(isLeftChild)
         parent.leftChild = current.leftChild;
      else
         parent.rightChild = current.leftChild;

   // if no left child, replace with right subtree
   else if(current.leftChild==null)
      if(current == root)
         root = current.rightChild;
      else if(isLeftChild)
         parent.leftChild = current.rightChild;
      else
         parent.rightChild = current.rightChild;

   else  // two children, so replace with inorder successor
      {
      // get successor of node to delete (current)
      Node successor = getSuccessor(current);

      // connect parent of current to successor instead
      if(current == root)
         root = successor;
      else if(isLeftChild)
         parent.leftChild = successor;
      else
         parent.rightChild = successor;

      // connect successor to current's left child
      successor.leftChild = current.leftChild;
      }  // end else two children
   // (successor cannot have a left child)
   return true;                                // success
   }  // end delete()
//-------------------------------------------------------------
// returns node with next-highest value after delNode
// goes to right child, then right child's left descendents
private Node getSuccessor(Node delNode)
   {
   Node successorParent = delNode;
   Node successor = delNode;
   Node current = delNode.rightChild;   // go to right child
   while(current != null)               // until no more
      {                                 // left children,
      successorParent = successor;
      successor = current;
      current = current.leftChild;      // go to left child
      }
                                        // if successor not
   if(successor != delNode.rightChild)  // right child,
      {                                 // make connections
      successorParent.leftChild = successor.rightChild;
      successor.rightChild = delNode.rightChild;
      }
   return successor;
   }
//-------------------------------------------------------------
public void traverse(int traverseType)
   {
   switch(traverseType)
      {
      case 1: System.out.print("\nPreorder traversal: ");
              preOrder(root);
              break;
      case 2: System.out.print("\nInorder traversal:  ");
              inOrder(root);
              break;
      case 3: System.out.print("\nPostorder traversal: ");
              postOrder(root);
              break;
      }
   System.out.println();
   }
//-------------------------------------------------------------
private void preOrder(Node localRoot)
   {
   if(localRoot != null)
      {
      System.out.print(localRoot.iData + " ");
      preOrder(localRoot.leftChild);
      preOrder(localRoot.rightChild);
      }
   }
//-------------------------------------------------------------
private void inOrder(Node localRoot)
   {
   if(localRoot != null)
      {
      inOrder(localRoot.leftChild);
      System.out.print(localRoot.iData + " ");
      inOrder(localRoot.rightChild);
      }
   }
//-------------------------------------------------------------
private void postOrder(Node localRoot)
   {
   if(localRoot != null)
      {
      postOrder(localRoot.leftChild);
      postOrder(localRoot.rightChild);
      System.out.print(localRoot.iData + " ");
      }
   }
//-------------------------------------------------------------
public void displayTree()
   {
   Stack globalStack = new Stack();
   globalStack.push(root);
   int nBlanks = 32;
   boolean isRowEmpty = false;
   System.out.println(
   "......................................................");
   while(isRowEmpty==false)
      {
      Stack localStack = new Stack();
      isRowEmpty = true;

      for(int j=0; j<nBlanks; j++)
         System.out.print(' ');

      while(globalStack.isEmpty()==false)
         {
         Node temp = (Node)globalStack.pop();
         if(temp != null)
            {
            System.out.print(temp.iData);
            localStack.push(temp.leftChild);
            localStack.push(temp.rightChild);

            if(temp.leftChild != null ||
                                temp.rightChild != null)
               isRowEmpty = false;
            }
         else
            {
            System.out.print("--");
            localStack.push(null);
            localStack.push(null);
            }
         for(int j=0; j<nBlanks*2-2; j++)
            System.out.print(' ');
         }  // end while globalStack not empty
      System.out.println();
      nBlanks /= 2;
      while(localStack.isEmpty()==false)
         globalStack.push( localStack.pop() );
      }  // end while isRowEmpty is false
   System.out.println(
   "......................................................");
   }  // end displayTree()
//-------------------------------------------------------------
}  // end class Tree
////////////////////////////////////////////////////////////////
class TreeApp
{
public static void main(String[] args) throws IOException
   {
   int value;
   Tree theTree = new Tree();

   theTree.insert(50, 1.5);
   theTree.insert(25, 1.2);
   theTree.insert(75, 1.7);
   theTree.insert(12, 1.5);
   theTree.insert(37, 1.2);
   theTree.insert(43, 1.7);
   theTree.insert(30, 1.5);
   theTree.insert(33, 1.2);
   theTree.insert(87, 1.7);
   theTree.insert(93, 1.5);
   theTree.insert(97, 1.5);

   while(true)
      {
      System.out.print("Enter first letter of show, ");
      System.out.print("insert, find, delete, or traverse: ");
      int choice = getChar();
      switch(choice)
         {
         case 's':
            theTree.displayTree();
            break;
         case 'i':
            System.out.print("Enter value to insert: ");
            value = getInt();
            theTree.insert(value, value + 0.9);
            break;
         case 'f':
            System.out.print("Enter value to find: ");
            value = getInt();
            Node found = theTree.find(value);
            if(found != null)
               {
               System.out.print("Found: ");
               found.displayNode();
               System.out.print("\n");
               }
            else
               System.out.print("Could not find ");
               System.out.print(value + '\n');
            break;
         case 'd':
            System.out.print("Enter value to delete: ");
            value = getInt();
            boolean didDelete = theTree.delete(value);
            if(didDelete)
               System.out.print("Deleted " + value + '\n');
            else
               System.out.print("Could not delete ");
               System.out.print(value + '\n');
            break;
         case 't':
            System.out.print("Enter type 1, 2 or 3: ");
            value = getInt();
            theTree.traverse(value);
            break;
         default:
            System.out.print("Invalid entry\n");
         }  // end switch
      }  // end while
   }  // end main()
//-------------------------------------------------------------
public static String getString() throws IOException
   {
   InputStreamReader isr = new InputStreamReader(System.in);
   BufferedReader br = new BufferedReader(isr);
   String s = br.readLine();
   return s;
   }
//-------------------------------------------------------------
public static char getChar() throws IOException
   {
   String s = getString();
   return s.charAt(0);
   }
//-------------------------------------------------------------
public static int getInt() throws IOException
   {
   String s = getString();
   return Integer.parseInt(s);
   }
//-------------------------------------------------------------
}  // end class TreeApp
////////////////////////////////////////////////////////////////