java 实现二叉树深度优先遍历的 前、中、后序遍历(递归)

import java.util.*;   
  
public class BinaryTree {   
    protected Node root;   
  
    public BinaryTree(Node root) {   
        this.root = root;   
    }   
  
    public Node getRoot() {   
        return root;   
    }   
  
    /** 构造树 */  
    public static Node init() {   
        Node a = new Node('A');   
        Node b = new Node('B', null, a);   
        Node c = new Node('C');   
        Node d = new Node('D', b, c);   
        Node e = new Node('E');   
        Node f = new Node('F', e, null);   
        Node g = new Node('G', null, f);   
        Node h = new Node('H', d, g);   
        return h;// root   
    }   
  
    /** 访问节点 */  
    public static void visit(Node p) {   
        System.out.print(p.getKey() + " ");   
    }   
  
    /** 递归实现前序遍历 */  
     static void preorder(Node p) {   
        if (p != null) {   
            visit(p);   
            preorder(p.getLeft());   
            preorder(p.getRight());   
        }   
    }   
  
    /** 递归实现中序遍历 */  
     static void inorder(Node p) {   
        if (p != null) {   
            inorder(p.getLeft());   
            visit(p);   
            inorder(p.getRight());   
        }   
    }   
  
    /** 递归实现后序遍历 */  
     static void postorder(Node p) {   
        if (p != null) {   
            postorder(p.getLeft());   
            postorder(p.getRight());   
            visit(p);   
        }   
    }   
   /** 层次遍历*/
   static void levelorder(Node p){   
        if(p==null) return;   
        Queue< Node> queue=new LinkedList< Node>();   
        queue.offer(p);   
        while(queue.size()>0){   
            Node temp=queue.poll();   
            visit(temp); 
            if(temp.getLeft()!=null){   
                queue.offer(temp.getLeft());   
            }   
            if(temp.getRight()!=null){   
                queue.offer(temp.getRight());   
            }   
        }   
       
    }   
  
  
    // 求二叉树的高度
 static int height(Node tree) {
    if (tree == null)
  return 0;
    else {
  int leftTreeHeight = height(tree.getLeft());
  int rightTreeHeight = height(tree.getRight());;
  return leftTreeHeight > rightTreeHeight ? leftTreeHeight + 1: rightTreeHeight + 1;
    }
}
// 求二叉树的结点总数
  static int nodes(Node tree) {
   if (tree == null)
  return 0;
   else {
  int left = nodes(tree.getLeft());
  int right = nodes(tree.getRight());
  return left + right + 1;
  }
}
// 求二叉树叶子节点的总数
 static int leaf(Node tree) {
   if (tree == null)
  return 0;
   else {
  int left = leaf(tree.getLeft());
  int right = leaf(tree.getRight());
  if (tree.getLeft() == null && tree.getRight() == null)
    return left + right + 1;
  else
    return left + right;
    }
 }
//将二叉树所有结点的左右子树交换
static void swapTree(Node root){
  if(root != null) {
   Node tmp = root.getLeft();
   root.setLeft(root.getRight());
   root.setRight(tmp);
   swapTree(root.getLeft());
   swapTree(root.getRight());
  }
}
     /** 
     * getLeafNodes: 递归求解给定二叉树的所有叶子结点 
     * @param root   给定二叉树的根结点 
     * @param leaflist 给定二叉树的所有叶子结点 
     */  
  static void  getLeafNodes(Node root, List< Node> leaflist)  
    {  
        if (root != null) {  
            if (root.getLeft() == null && root.getRight() == null) {  
                leaflist.add(root);  
                return ;  
            }  
            getLeafNodes(root.getLeft(), leaflist);  
            getLeafNodes(root.getRight(), leaflist);  
        }  
    }  
  
  /** 
     * longestPath: 递归求解给定二叉树的一条最长路径 如果有多条，输出其中一条
     * @param root  给定二叉树的根结点 
     * @param longestPath 存放二叉树的最长路径上的结点 
     */  
    static void longestPath(Node root, List< Node> longestPath)  
    {  
        if (root != null) {  
            longestPath.add(root);  
            if (root.getLeft() == null && root.getRight() == null) { // 左右子树均空  
                 return ;  
            }  
         
                List< Node> leftLongestPath = new ArrayList< Node>();  
                List< Node> rightLongestPath = new ArrayList< Node>();  
                longestPath(root.getLeft(), leftLongestPath);  
                longestPath(root.getRight(), rightLongestPath);  
                if (leftLongestPath.size() >= rightLongestPath.size()) {  
                    longestPath.addAll(leftLongestPath);  
                } else if (leftLongestPath.size() < rightLongestPath.size()) {  
                    longestPath.addAll(rightLongestPath);  
                                
            }  
        }  
    }  
 
    /**  
     * @param args  
     */  
    public static void main(String[] args) {   
        BinaryTree tree = new BinaryTree(init());   
        System.out.print(" 前序遍历:");   
        preorder(tree.getRoot());   
        System.out.println();   
        System.out.print(" 中序遍历:");   
        inorder(tree.getRoot());   
        System.out.println();   
        System.out.print(" 后序遍历:");   
        postorder(tree.getRoot());   
        System.out.println(); 
        System.out.println(); 
       
        System.out.println("层次遍历");
        levelorder(tree.getRoot());
        System.out.println();   
        System.out.println();   
         System.out.println("叶子结点数");
         System.out.println(leaf(tree.getRoot()));
         System.out.println("总结点数");
         System.out.println(nodes(tree.getRoot()));
         System.out.println("树的高度");
         System.out.println(height(tree.getRoot()));
     
    }    
  
}  
public class Node {   
    private char key;   
    private Node left, right;   
  
    public Node(char key) {   
        this(key, null, null);   
    }   
  
    public Node(char key, Node left, Node right) {   
        this.key = key;   
        this.left = left;   
        this.right = right;   
    }   
  
    public char getKey() {   
        return key;   
    }   
  
    public void setKey(char key) {   
        this.key = key;   
    }   
  
    public Node getLeft() {   
        return left;   
    }   
  
    public void setLeft(Node left) {   
        this.left = left;   
    }   
  
    public Node getRight() {   
        return right;   
    }   
  
    public void setRight(Node right) {   
        this.right = right;   
    }   
}