二叉树的递归遍历和非递归遍历（附详细例子）
转：http://blog.csdn.net/sheepmu/article/details/28941285
二叉树的递归遍历和非递归遍历（附详细例子）
二叉树的遍历主要有递归实现和非递归实现，递归实现比较好理解，非递归实现主要是利用了栈的思想，后进先出，本文实现二叉树的非递归遍历主要是用了LinkedList可以当做栈使用的功能。具体例子如下：
import java.util.LinkedList;
public class BinaryTree
{
private TreeNode root;// 根节点
public BinaryTree()
{
}
public BinaryTree(TreeNode root)
{
this.root = root;
}
public TreeNode getRoot()
{
return root;
}
public void setRoot(TreeNode root)
{
this.root = root;
}
/**
* 节点类
*/
private static class TreeNode
{
private String data = null;// 数据部分
private TreeNode left;// 左节点的引用
private TreeNode right;// 右节点的引用
public TreeNode(String data, TreeNode left, TreeNode right)//节点的构造函数，测试函数中创建节点就是用了它
{
this.data = data;
this.left = left;
this.right = right;
}
public String getData()//节点类的get和set方法
{
return data;
}
public void setData(String data)
{
this.data = data;
}
public TreeNode getLeft()
{
return left;
}
public void setLeft(TreeNode left)
{
this.left = left;
}
public TreeNode getRight()
{
return right;
}
public void setRight(TreeNode right)
{
this.right = right;
}
}
/**
* 递归 前续遍历
*/
public void preOrder(TreeNode node)
{
if (node != null)
{
System.out.print(node.getData()+" ");
preOrder(node.getLeft());
preOrder(node.getRight());
}
}
/**
* 递归 中续遍历
*/
public void inOrder(TreeNode node)
{
if (node != null)
{
inOrder(node.getLeft());
System.out.print(node.getData()+" ");
inOrder(node.getRight());
}
}
/**
* 递归 后续遍历
*/
public void postOrder(TreeNode node)
{
if (node != null)
{
postOrder(node.getLeft());
postOrder(node.getRight());
System.out.print(node.getData()+" ");
}
}
/**
* 非递归 前续遍历
*/
public void preOrderNoRecursion()
{
LinkedList<TreeNode> stack = new LinkedList<TreeNode>();
stack.push(root);
TreeNode current = null;
while (!stack.isEmpty())
{
current = stack.pop();
System.out.print(current.data+" ");
if (current.getRight() != null)
stack.push(current.getRight());
if (current.getLeft() != null)
stack.push(current.getLeft());
}
System.out.println();
}
/**
* 非递归 中续遍历
*/
public void inorderNoRecursion()
{
LinkedList<TreeNode> stack = new LinkedList<TreeNode>();
TreeNode current = root;
while (current != null || !stack.isEmpty())
{
while(current != null)
{
stack.push(current);
current = current.getLeft();
}
if (!stack.isEmpty())
{
current = stack.pop();
System.out.print(current.data+" ");
current = current.getRight();
}
}
System.out.println();
}
/**
* 非递归 后续遍历
*/
public void postorderNoRecursion()
{
TreeNode rNode = null;
TreeNode current = root;
LinkedList<TreeNode> stack = new LinkedList<TreeNode>();
while(current != null || !stack.isEmpty())
{
while(current != null)
{
stack.push(current);
current = current.getLeft();
}
current = stack.pop();
while (current != null && (current.getRight() == null ||current.getRight() == rNode))
{
System.out.print(current.data+" ");
rNode = current;
if (stack.isEmpty())
{
System.out.println();
return;
}
current = stack.pop();
}
stack.push(current);
current = current.getRight();
}
}
public static void main(String[] args)
{
TreeNode l2 = new TreeNode("E", null, null);//这五行构造一棵二叉树
TreeNode r2 = new TreeNode("D", null, null);
TreeNode l1 = new TreeNode("B",null, r2);// 根节点左子树
TreeNode r1 = new TreeNode("C", l2, null);// 根节点右子树
TreeNode root = new TreeNode("A", l1, r1);// 创建根节点
BinaryTree bt = new BinaryTree(root);
System.out.print(" 递归 前序遍历------->");
bt.preOrder(bt.getRoot());
System.out.print(" 非递归 前序遍历------->");
bt.preorderNoRecursion();
System.out.print(" 递归 中序遍历------->");
bt.inOrder(bt.getRoot());
System.out.print(" 非递归 中序遍历------->");
bt.inorderNoRecursion();
System.out.print(" 递归 后序遍历------->");
bt.postOrder(bt.getRoot());
System.out.print(" 非递归 后序遍历------->");
bt.postorderNoRecursion();
}
}
递归 前序遍历------->A B D C E 非递归 前序遍历------->A B D C E
递归 中序遍历------->B D A E C 非递归 中序遍历------->B D A E C
递归 后序遍历------->D B E C A 非递归 后序遍历------->D B E C A