二叉树三种遍历的非递归实现

import java.util.Stack;

class TreeNode<K> {
TreeNode<K> left, right;
K key;
public TreeNode(K k) {
left = null; right = null; key = k;
}
}

class BinaryTree<K extends Comparable<K> > { //添加 extends Comparable<K>后，K对象可以进行比较。
TreeNode<K> root;
public BinaryTree() {
root = null;
}
public void createTree(TreeNode<K> node, K data) { //建立二叉树
if(root == null) {
root = new TreeNode<K>(data);
} else {
if(data.compareTo(node.key) < 0) {
if(node.left == null)
node.left = new TreeNode<K>(data);
else
createTree(node.left, data);
} else {
if(node.right == null)
node.right = new TreeNode<K>(data);
else
createTree(node.right, data);
}
}
}
public void preOrder(TreeNode<K> root) { // 前序遍历，非递归实现。
if(root != null) {
Stack<TreeNode<K>> stack = new Stack<TreeNode<K>>();
stack.push(root);
while (!stack.isEmpty()) {
TreeNode<K> tmp = stack.pop();
System.out.println(tmp.key);
if(tmp.right != null) stack.push(tmp.right);
if(tmp.left != null) stack.push(tmp.left);
}
}
}
public void inOrder(TreeNode<K> root) { //中序遍历，非递归实现
Stack<TreeNode<K>> stack = new Stack<TreeNode<K>>();
while (root != null || !stack.isEmpty()) {
while(root != null) {
stack.push(root);
root = root.left;
}
if (!stack.isEmpty()) {
TreeNode<K> tmp = stack.pop();
System.out.println(tmp.key);
root = tmp.right;
}
}
}
public void postOrder(TreeNode<K> root) { //后序遍历，非递归实现
Stack<TreeNode<K>> stack = new Stack<TreeNode<K>>();
TreeNode<K> pre = root;                         //记录上一个输出的节点。
while (root != null || !stack.isEmpty()) {
while (root != null) {
stack.push(root);
root = root.left;
}
if (!stack.isEmpty()) {
TreeNode<K> tmp = stack.peek().right;
if(tmp == null || tmp == pre) {
TreeNode<K> tmp2 = stack.pop();
System.out.println(tmp2.key);
pre = tmp2;
root = null;
} else {
root = tmp;
}
}
}
}
}
class People implements Comparable<People> { // 自定义People类，并覆盖了equals,hashCode,toString方法，实现了Comparable接口。
String name;
int age;
public People(String n, int a) {
name = n; age = a;
}
@Override
public boolean equals(Object obj) {
if(this == obj)
return true;
if(!(obj instanceof People))
return false;
return this.name.equals(((People)obj).name) && this.age == ((People)obj).age;
}
@Override
public int hashCode() {
return name.hashCode()*37 + age;
}
@Override
public String toString() {
return name + "," + age;
}
@Override
public int compareTo(People o) {
return this.age - o.age;
}
}
public class TestClass {
public static void main(String[] args) {//6, 8, 7, 5, 2, 5
People[] people = new People[] { new People("xue", 6),
new People("hong", 8), new People("jun", 7), new People("shang", 5),
new People("hai", 2), new People("bei", 5)};
BinaryTree<People> bt = new BinaryTree<People>();
for (int i = 0; i < people.length; i++) {
bt.createTree(bt.root, people[i]);
}
//        bt.preOrder(bt.root);
//        bt.inOrder(bt.root);
bt.postOrder(bt.root);
}
}