二叉树的遍历(递归与非递归）

节点类 Node.java

package com.shundong.btree;
/**
 * 链式二叉树节点
 * @author shundong106
 *
 */
public class Node {
	Object value;
	Node leftChild;
	Node rightChild;
	public Node(int value) {
		super();
		this.value = value;
	}
	public Node(int value, Node leftChild, Node rightChild) {
		super();
		this.value = value;
		this.leftChild = leftChild;
		this.rightChild = rightChild;
	}
	
}

　方法一 递归 

package com.shundong.btree;
/**
 * 方法1 递归
 * @author shundong106
 *
 */
public class TraversalOfBinaryTree {
	private Node root;//根节点

	public TraversalOfBinaryTree() {
		super();
		// TODO Auto-generated constructor stub
	}
	public TraversalOfBinaryTree(Node root) {
		super();
		this.root = root;
	}
	//二叉树先序遍历
	public void preorderTraversal() {
		System.out.print("先根遍历");
		this.preorderTraversal(root);
		System.out.println();
	}
	//先序遍历的辅助函数
	private void preorderTraversal(Node root) {
		if(root !=null) {
			//输出根
			System.out.print(root.value+" ");
			//遍历根的 左子树
			this.preorderTraversal(root.leftChild);
			//遍历根的 右子树
			this.preorderTraversal(root.rightChild);
		}
	}
	//二叉树中序遍历
	public void inOrderTraversal() {
		System.out.print("中序遍历");
		this.inOrderTraversal(root);
		System.out.println();
	}
	private void inOrderTraversal(Node root) {
		if(root !=null) {
			//先输出左子树
			this.inOrderTraversal(root.leftChild);
			//输出根
			System.out.print(root.value+" ");
			//再输出右子树
			this.inOrderTraversal(root.rightChild);
		}
	}
	//二叉树的后根遍历
	public void postOrderTraversal() {
		System.out.print("后根遍历");
		this.postOrderTraversal(root);
		System.out.println();
	}
	private void postOrderTraversal(Node root) {
		if(root !=null) {
			//先遍历左子树
			this.postOrderTraversal(root.leftChild);
			//在输出右子树
			this.postOrderTraversal(root.rightChild);
			//再输出根
			System.out.print(root.value+" ");
		}
	}
}

　　方法二 非递归(栈）

package com.shundong.btree;

import java.util.Deque;
import java.util.LinkedList;

/**
 * ！递归
 * @author shundong106
 *
 */
public class TraversalOfBinaryTree2 {
	private Node root;//根节点

	public TraversalOfBinaryTree2() {
		super();
		// TODO Auto-generated constructor stub
	}
	public TraversalOfBinaryTree2(Node root) {
		super();
		this.root = root;
	}
	//二叉树先序遍历 非递归
	public void preOrderTraversal() {
		System.out.print("先根遍历");
		this.preOrderTraversal(root);
		System.out.println();
	}
	//先序遍历的辅助函数
	private void preOrderTraversal(Node root) {
		//创建一个栈
		Deque<Node> stack = new LinkedList<Node>(); 
		while (root != null || !stack.isEmpty()) {    
			while (root != null) {    
				//先直接输出 根节点
				System.out.print(root.value+" ");    
				stack.push(root);//将根节点入栈
				root = root.leftChild;//将当前根节点的做孩子 当做新的 根节点
			}    
			if (!stack.isEmpty()) {    
				root = stack.pop();    
				root = root.rightChild;
			}    
		}    
	}
	//二叉树中序遍历递归
	public void inOrderTraversal() {
		System.out.print("中序遍历");
		this.inOrderTraversal(root);
		System.out.println();
	}
	private void inOrderTraversal(Node root) {
		//创建一个栈
		Deque<Node> stack = new LinkedList<Node>();
		//将根节点 赋值
		Node current = root ;
		while(current !=null || !stack.isEmpty()) {
			while(current !=null) {
				stack.push(current);//让根进栈 
				current = current.leftChild;//然后再遍历左子树 只有到达二叉树的左叶子 才会终止循环
			}
			//此刻若栈不为空 那么栈顶必定是 根节点
			if(!stack.isEmpty()) {
				current = stack.pop();//输出当前的栈顶 也就是 左叶子节点
				System.out.print(current.value+" ");
				current = current.rightChild;//然后此刻开始遍历右子树
			}
		}
	}
	//二叉树的后根遍历
	public void postOrderTraversal() {
		System.out.print("后根遍历");
		this.postOrderTraversal(root);
		System.out.println();
	}
	private void postOrderTraversal(Node root) {
		Deque<Node> stack = new LinkedList<Node>(); 
		Deque<Integer> stack2 = new LinkedList<Integer>();    
        Integer i = new Integer(1);    
        while (root != null || !stack.isEmpty()) {    
            while (root != null) {    
                stack.push(root);    
                stack2.push(new Integer(0));    
                root = root.leftChild;    
            }    
            while (!stack.isEmpty() && stack2.peek().equals(i)) {    
                stack2.pop();    
                System.out.print(stack.pop().value +" ");    
            }    
    
            if (!stack.isEmpty()) {    
                stack2.pop();    
                stack2.push(new Integer(1));    
                root = stack.peek();    
                root = root.rightChild; 
            }    
        }    
	}
}

　　

测试类 Test.java

package com.shundong.btree;
/**
 * 二叉树遍历的测试类
 * @author shundong
 *
 */
public class Test {
	public static void main(String[] args) {
		Node node5 = new Node(5,null,null);
		Node node4 = new Node(4,null,node5);
		Node node7 = new Node(7,null,null);
		Node node6 = new Node(6,null,node7);
		Node node3 = new Node(3,null,null);
		Node node2 = new Node(2, node3, node6);
		Node node1 = new Node(1, node4, node2);//根节点
		TraversalOfBinaryTree btree = new TraversalOfBinaryTree(node1);
		//先根遍历
		btree.preorderTraversal();
		//中根遍历
		btree.inOrderTraversal();
		//后根遍历
		btree.postOrderTraversal();
		System.out.println("-------------------------非递归——————————————————————");
		TraversalOfBinaryTree2 btree2 = new TraversalOfBinaryTree2(node1);
		btree2.preOrderTraversal();
		btree2.inOrderTraversal();
		btree2.postOrderTraversal();
	
	}
}