非递归的二叉树遍历（Java实现）

import java.util.Stack;

public class TreeDLR {
public static void run(TreeNode node){
Stack<TreeNode> stack = new Stack<>();
while(node != null || !stack.isEmpty()){
if(node != null){
System.out.print(node.data+" ");
stack.push(node);
node = node.left;
}else {
node = stack.pop();
node = node.right;
}
}
}
}

import java.util.Stack;

public class TreeLDR {
public static void run(TreeNode node){
Stack<TreeNode> stack = new Stack<>();
while(node != null || !stack.isEmpty()){
if(node != null){
stack.push(node);
node = node.left;
}else{
node = stack.pop();
System.out.print(node.data + " ");
node = node.right;
}
}
}
}

import java.util.Stack;

public class TreeLRD {
public static void run(TreeNode node){
Stack<TreeNode> stack = new Stack<>();
TreeNode last = null;
while(node != null || !stack.isEmpty()){
if(node != null){
stack.push(node);
node = node.left;
}else{
node = stack.peek();
if(node.right != null && node.right != last){
node = node.right;
}else{
System.out.print(node.data + " ");
stack.pop();
last = node;
node = null;
}
}
}
}
}

import java.util.ArrayDeque;

public class TreeLevel {
public static void run(TreeNode node){
ArrayDeque<TreeNode> queue = new ArrayDeque<>();
queue.add(node);
while(!queue.isEmpty()){
node = queue.poll();
System.out.print(node.data + " ");
if(node.left != null) queue.add(node.left);
if(node.right != null) queue.add(node.right);
}
}
}