二叉树的遍历

1.结点类

package edu.tcu.soft.binary;public class BinaryNode {private int value;private BinaryNode left;private BinaryNode right;public int getValue() {return value;}public void setValue(int value) {this.value = value;}public BinaryNode getLeft() {return left;}public void setLeft(BinaryNode left) {this.left = left;}public BinaryNode getRight() {return right;}public void setRight(BinaryNode right) {this.right = right;}    public BinaryNode(int value, BinaryNode left, BinaryNode right) {super();this.value = value;this.left = left;this.right = right;}    public BinaryNode() {}    public BinaryNode(int value) {this.left=null;this.right=null;this.value=value;}}

2.二叉树类

<pre name="code" class="java">package edu.tcu.soft.binary;import java.util.LinkedList;import java.util.Queue;import java.util.Stack;public class BinaryTree {public BinaryTree() {}// 插入结点public void insert(BinaryNode root, int data) {if (data > root.getValue()) // 二叉树的左节点都比根节点小{if (root.getRight() == null) {root.setRight(new BinaryNode(data));} else {this.insert(root.getRight(), data);}} else { // 二叉树的右节点都比根节点大if (root.getLeft() == null) {root.setLeft(new BinaryNode(data));} else {this.insert(root.getLeft(), data);}}}// 前序遍历public void preOrder(BinaryNode root) {// -------------------1.递归// if (root == null) {// return;// } else {// System.out.print(root.getValue() + " ");// 输出结点的数据域// preOrder(root.getLeft()); // 遍历左子树// preOrder(root.getRight());//遍历右子树// }// -----------------2.非递归Stack<BinaryNode> stack = new Stack<BinaryNode>();while (root != null || !stack.empty())// 当根节点为空或者栈为空才跳出循环{while (root != null) {System.out.print(root.getValue() + "  ");stack.push(root);root = root.getLeft();}if (!stack.empty()) {root = stack.pop();root = root.getRight();}}}// 中序遍历public void inOrder(BinaryNode root) {// ----------------1.递归//if (root == null)//return;//else {//inOrder(root.getLeft());//System.out.print(root.getValue() + "  ");//inOrder(root.getRight());//}// -----------------2.非递归Stack<BinaryNode> stack = new Stack<BinaryNode>();BinaryNode s = new BinaryNode();while (root != null || !stack.empty()) {while (root != null) {stack.push(root);root = root.getLeft();}if (!stack.empty()) {s = stack.pop();System.out.print(s.getValue() + " ");root = s.getRight();}}}// 后序遍历public void postOrder(BinaryNode root) {//--------------递归// if(root==null)//return;//else{//postOrder(root.getLeft());//postOrder(root.getRight());//System.out.println(root.getValue());//}// ---------------非递归 ----使用了两个栈Stack<BinaryNode> stack = new Stack<BinaryNode>();Stack<Integer> stack2 = new Stack<Integer>();Integer i = new Integer(1);while (root != null || !stack.empty()) {while (root != null) {stack.push(root);stack2.push(new Integer(0));root = root.getLeft();}while (!stack.empty() && stack2.peek().equals(i)) {stack2.pop();System.out.print(stack.pop().getValue() + "  ");}if (!stack.empty()) {stack2.pop();stack2.push(new Integer(1));root = stack.peek();root = root.getRight();}}// ---------------------非递归 --------使用一个栈                //还没实现    待续}// 层序遍历public void levelOrder(BinaryNode root) {if (root == null)return;else {Queue<BinaryNode> queue = new LinkedList<BinaryNode>();queue.add(root);while (!queue.isEmpty()) {BinaryNode node = queue.remove();System.out.print(node.getValue() + "-");if (node.getLeft() != null)queue.add(node.getLeft());if (node.getRight() != null)queue.add(node.getRight());}}}// 释放结点public void release(BinaryNode node) {if (node == null)return;else {release(node.getLeft());release(node.getRight());node = null;}}}

3.测试类

package edu.tcu.soft.binary;public class Test {   public static void main(String[] args) {      int a[]={10,12,9,8,15,14};   BinaryNode root=new BinaryNode(a[0]);   BinaryTree tree=new BinaryTree();   for(int i=1;i<a.length;i++){    tree.insert(root, a[i]);       //向二叉树中插入数据   }   //   tree.preOrder(root);//   System.out.println();//   tree.inOrder(root);//   System.out.println();   tree.levelOrder(root);}}

其实，这是我第一次用java写关于数据结构的东西，在写这个的时候，遇到了空指针异常，就是在遍历的时候只打印了根节点的值，其他的节点打印不出，而且还报空指针异常，最后我才发现我在为左右字树赋值的时候，没有给左右子树实例化。我居然忘了在使用对象之前需要实例化的。