二叉树的遍历（Java实现）

package util;

import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.List;
import java.util.Queue;

public class BinaryNode<T> {
/**
* 泛型BinaryNode类
*/
public T item;

public BinaryNode<T> left,right;//左右子树

public BinaryNode(T item)
{
this.item = item;
left = right = null;
}
public BinaryNode (T item, BinaryNode<T> left, BinaryNode<T> right)
{
this.item = item;
this.left = left;
this.right = right;
}

public T getNodeValue() {
return item;
}
public void setNodeValue(T item) {
this.item = item;
}
public BinaryNode<T> getLeft() {
return left;
}
public void setLeft(BinaryNode<T> left) {
this.left = left;
}
public BinaryNode<T> getRight() {
return right;
}
public void setRight(BinaryNode<T> right) {
this.right = right;
}

//判断是否为叶子
public boolean isLeaf(){
return (left==null)&&(right==null);
}

//前序遍历二叉树(递归)
public List<BinaryNode<T>> toStringPreorder(BinaryNode<T> node){
List<BinaryNode<T>> list=new ArrayList<BinaryNode<T>>();
list.add(node);
if (node.left!=null) {
list.addAll(toStringPreorder(node.left));
}
if (node.right!=null) {
list.addAll(toStringPreorder(node.right));
}
return list;
}
//前序遍历二叉树(非递归)
public List<BinaryNode<T>> toStringPreorderNoRec(BinaryNode<T> node){
List<BinaryNode<T>> list=new ArrayList<BinaryNode<T>>();
ArrayDeque<BinaryNode<T>> stack=new ArrayDeque<BinaryNode<T>>();
while ((node!=null)||!stack.isEmpty()) {
if (node!=null) {
list.add(node);
stack.push(node);
node=node.left;
} else {
node=stack.peek();
stack.pop();
node=node.right;
}
}
return list;
}

//中序遍历二叉树
public List<BinaryNode<T>> toStringInorder(BinaryNode<T> node){
List<BinaryNode<T>> list=new ArrayList<BinaryNode<T>>();
if (node.left!=null) {
list.addAll(toStringPreorder(node.left));
}
list.add(node);
if (node.right!=null) {
list.addAll(toStringPreorder(node.right));
}
return list;
}
//中序遍历二叉树(非递归)
public List<BinaryNode<T>> toStringInorderNoRec(BinaryNode<T> node){
List<BinaryNode<T>> list=new ArrayList<BinaryNode<T>>();
ArrayDeque<BinaryNode<T>> stack=new ArrayDeque<BinaryNode<T>>();
while ((node!=null)||!stack.isEmpty()) {
if (node!=null) {
stack.push(node);
node=node.left;
} else {
node=stack.peek();
list.add(node);
stack.pop();
node=node.right;
}
}
return list;
}

//后序遍历二叉树
public String toStringPostorder(){
String result="";
if (left!=null) {
result += left.toStringPostorder();
}
if (right!=null) {
result += right.toStringPostorder();
}
result += item;
return result;
}
//后序遍历二叉树(非递归)
/**
* 先遍历树的逆后序遍历(根、右、左),在翻转逆后序遍历就是后序遍历二叉树(左、右、根)
* @return result栈
*/
public ArrayDeque<BinaryNode<T>> toStringPostorderNoRec(BinaryNode<T> node){
ArrayDeque<BinaryNode<T>> stack=new ArrayDeque<BinaryNode<T>>();
ArrayDeque<BinaryNode<T>> result=new ArrayDeque<BinaryNode<T>>();
while ((node!=null)||!stack.isEmpty()) {
if (node!=null) {
result.push(node);
stack.push(node);
node=node.right;
} else {
node=stack.peek();
stack.pop();
node=node.left;
}
}
return result;
}
//后序遍历二叉树2(非递归)
/**
* 要保证根结点在左孩子和右孩子访问之后才能访问，因此对于任一结点P，先将其入栈。如果P不存在左孩子和右孩子，则可以直接访问它；
* 或者P存在左孩子或者右孩子，但是其左孩子和右孩子都已被访问过了，则同样可以直接访问该结点。若非上述两种情况，
* 则将P的右孩子和左孩子依次入栈，这样就保证了每次取栈顶元素的时候，左孩子在右孩子前面被访问，左孩子和右孩子都在根结点前面被访问。
* @return result栈
*/
public ArrayList<BinaryNode<T>> toStringPostorderNoRec2(BinaryNode<T> root){
ArrayDeque<BinaryNode<T>> stack=new ArrayDeque<BinaryNode<T>>();
ArrayList<BinaryNode<T>> result=new ArrayList<BinaryNode<T>>();
BinaryNode<T> curr;//当前栈顶指针
BinaryNode<T> pre=null;//前一次访问节点
stack.push(root);
while (!stack.isEmpty()) {
curr=stack.peek();
if ((curr.left==null&&curr.right==null)||(pre!=null&&(pre==curr.left||pre==curr.right))) {
result.add(curr);//输出结果
stack.pop();
pre=curr;
} else {
if (curr.right!=null) {
stack.push(curr.right);
}
if (curr.left!=null) {
stack.push(curr.left);
}
}
}
return result;
}

//层序遍历(广度优先遍历)
public List<BinaryNode<T>> toStringLevelOrder(){
List<BinaryNode<T>> list=new ArrayList<BinaryNode<T>>();
Queue<BinaryNode<T>> queue=new ArrayDeque<BinaryNode<T>>();
queue.offer(this);//root
while (!(queue.isEmpty())) {
list.add(queue.peek());
BinaryNode<T> node=queue.poll();
if (node.left != null) {
queue.offer(node.left);
}
if (node.right != null) {
queue.offer(node.right);
}
}
return list;
}

}