（转）java语言实现二叉树的前序、中序与后序遍历(递归与非递归)

http://blog.csdn.net/chj97/article/details/6845824

import java.util.*;
public class BinaryTree {
 private BinaryTree lchild;
 private BinaryTree rchild;
 private Object data;
 /**
  * @param args
  */
 public BinaryTree(BinaryTree l, BinaryTree r, Object data) {
  lchild = l;
  rchild = r;
  this.data = data;
 }
 public static void main(String[] args) {
  // TODO Auto-generated method stub
  BinaryTree  G= new BinaryTree(null, null, 'G');
  BinaryTree  H= new BinaryTree(null, null, 'H');
  BinaryTree  F= new BinaryTree(G, H, 'F');
  BinaryTree  D= new BinaryTree(null, F, 'D');
  BinaryTree  E= new BinaryTree(null, null, 'E');
  BinaryTree  B= new BinaryTree(D, E,  'B');
  BinaryTree  C= new BinaryTree(null, null, 'C');
  BinaryTree A = new BinaryTree(B, C, 'A');
  
  System.out.println("先序遍历。。。。。。。"); 
  pre(A);
        System.out.println(); 
       
        System.out.println("中序遍历。。。。。。。"); 
  in(A);
       System.out.println(); 
        
        System.out.println("后序遍历。。。。。。。"); 
  post(A);
       System.out.println(); 
        
        System.out.println("非递归先序遍历。。。。。。。"); 
  preTraverse(A);
        System.out.println(); 
        
        System.out.println("非递归中序遍历。。。。。。。"); 
  inTraverse(A);
        System.out.println(); 
        
        System.out.println("非递归后序遍历。。。。。。。"); 
  postTraverse(A);
        System.out.println(); 
        
        System.out.println("非递归后序遍历2。。。。。。。"); 
        postTraverse2(A);
        System.out.println(); 
 }
 
 public static void visit(BinaryTree bt) {
  System.out.print(bt.data + " ");
 }
 
 //递归先序遍历
 public static void pre(BinaryTree root) {
  if(root == null)return;
  visit(root);
  if(root.lchild != null)pre(root.lchild);
  if(root.rchild != null)pre(root.rchild);
 }
 
 //递归中序遍历
 public static void in(BinaryTree root) {
  if(root == null)return;
  if(root.lchild != null)in(root.lchild);
  visit(root);
  if(root.rchild != null)in(root.rchild);
 }
 
 //递归后序遍历
 public static void post(BinaryTree root) {
  if(root == null)return;
  if(root.lchild != null)post(root.lchild);
  if(root.rchild != null)post(root.rchild);
  visit(root);
 }
 
 //非递归先序遍历
 public static void preTraverse(BinaryTree root) {
  Stack s = new Stack();
  s.push(root);
  while(!s.isEmpty()) {
   BinaryTree bt = (BinaryTree)s.pop();
   visit(bt);
   if(bt.rchild != null) s.push(bt.rchild);
   if(bt.lchild != null) s.push(bt.lchild);
  }
 }
 
 //非递归中序遍历
 public static void inTraverse(BinaryTree root) {
  Stack s = new Stack();
  BinaryTree p = root;
  while(p!=null || !s.isEmpty()) {
   if(p!=null) {
    s.push(p);
    p = p.lchild;
   }
   else {
    p = (BinaryTree)s.pop();
    visit(p);
    p = p.rchild;
   }
  }
 }
 
 //非递归后序遍历
 public static void postTraverse(BinaryTree root) {
  Stack s = new Stack();
  BinaryTree p = root;
  //pre标记最近出栈的节点，用于判断是否是p节点的右孩子，如果是的话，就可以访问p节点
  BinaryTree pre = p;
  //flag标记是出栈还是继续将左孩子进栈
  boolean flag = true;
  while(p!=null || !s.isEmpty()) {
   if(p!=null && flag) {
    s.push(p);
    p = p.lchild;
   }
   else {
    if(s.isEmpty()) return;
    p = (BinaryTree)s.peek();
    if(p.rchild != null && p.rchild!=pre) {
     p = p.rchild;
     flag = true;
    }
    else {
     p = (BinaryTree)s.pop();
     visit(p);
     flag = false;
     pre = p;
    }
   }
  }
 }
 
 //非递归后序遍历2
 public static void postTraverse2(BinaryTree root) {
  Stack s = new Stack();
  BinaryTree p = root;
  //pre标记最近出栈的节点，用于判断是否是p节点的右孩子，如果是的话，就可以访问p节点
  BinaryTree pre = p;
  while(p!=null || !s.isEmpty()) {
   if(p!=null) {
    s.push(p);
    p = p.lchild;
   }
   else {
    if(s.isEmpty()) return;
    p = (BinaryTree)s.peek();
    if(p.rchild != null && p.rchild!=pre) {
     p = p.rchild;
    }
    else {
     p = (BinaryTree)s.pop();
     visit(p);
     pre = p;
     p = null;
    }
   }
  }
 }
}