用Java实现二叉树前序遍历、中序遍历和后序遍历。

public class BinaryTree {

private Node root;

/**
*
* 内部节点类
*
* @author yhh
*/
private class Node {
private Node left;
private Node right;
private int data;

public Node(int data) {
this.left = null;
this.right = null;
this.data = data;
}
}

public BinaryTree() {
root = null;
}

/**
* 递归创建二叉树
*
* @param node
* @param data
*/
public void buildTree(Node node, int data) {
if (root == null) {
root = new Node(data);
}
else {
if (data < node.data) {
if (node.left == null) {
node.left = new Node(data);
}
else {
buildTree(node.left, data);
}
}
else {
if (node.right == null) {
node.right = new Node(data);
}
else {
buildTree(node.right, data);
}
}
}
}

/**
* 前序遍历
*
* @param node
*/
public void leftOrder(Node node) {
if (node != null) {
System.out.print(node.data + "  ");
leftOrder(node.left);
leftOrder(node.right);
}
}

/**
* 中序遍历
*
* @param node
*/
public void middleOrder(Node node) {
if (node != null) {
middleOrder(node.left);
System.out.print(node.data + "  ");
middleOrder(node.right);
}
}

/**
* 后序遍历
*
* @param node
*/
public void rightOrder(Node node) {
if (node != null) {
rightOrder(node.left);
rightOrder(node.right);
System.out.print(node.data + "  ");
}
}

public static void main(String[] args) {
int[] a = { 12, 43, 12, 45, 2, 9, 11 };
BinaryTree bTree = new BinaryTree();

for (int i = 0; i < a.length; i++) {
bTree.buildTree(bTree.root, a[i]);
}

System.out.print("\n前序遍历 ： ");
bTree.leftOrder(bTree.root);
System.out.print("\n中 序遍历 ： ");
bTree.middleOrder(bTree.root);
System.out.print("\n后 序遍历 ： ");
bTree.rightOrder(bTree.root);
}

}