实现二叉树的先序、 中序、 后序遍历， 包括递归方式和非递归方式

实现二叉树的先序、 中序、 后序遍历， 包括递归方式和非递归方式

package BinaryTree;

import java.util.Stack;

public class PreInPosTraverasl {
    public static class Node{
        public int value;
        public Node left;
        public Node right;
        public Node(int data){ this.value=data; }
    }

    public static void preOrderRecur(Node root){
        if (root == null){
            return;
        }
        System.out.print(root.value+" ");
        preOrderRecur(root.left);
        preOrderRecur(root.right);
    }

    public static void inOrderRecur(Node root){
        if (root == null){
            return;
        }
        inOrderRecur(root.left);
        System.out.print(root.value+" ");
        inOrderRecur(root.right);
    }

    public static void posOrderRecur(Node root){
        if (root == null){
            return;
        }
        posOrderRecur(root.left);
        posOrderRecur(root.right);
        System.out.print(root.value+" ");
    }

    public static void preOrderUnRecur(Node root){
        System.out.print("pre-order: ");
        if (root != null){
            Stack<Node> stack=new Stack<>();
            stack.add(root);
            Node temp=null;
            while (!stack.isEmpty()){
                temp=stack.pop();
                System.out.print(temp.value+" ");
                if (temp.right!=null){
                    stack.push(temp.right);
                }
                if (temp.left!=null){
                    stack.push(temp.left);
                }
            }
        }
        System.out.println();
    }

    public static void inOrderUnRecur(Node root){
        System.out.print("in-order: ");
        if (root != null){
            Stack<Node> stack=new Stack<>();
            Node cur=root;
            while (!stack.isEmpty() || cur!= null){
                if (cur!=null){
                    stack.push(cur);
                    cur=cur.left;
                }else {
                    cur=stack.pop();
                    System.out.print(cur.value+" ");
                    cur=cur.right;
                }
            }
        }
        System.out.println();
    }

    public static void posOrderUnRecur(Node root){
        System.out.print("pos-order: ");
        if (root != null){
            Stack<Node> stack=new Stack<>();
            Stack<Node> stack1=new Stack<>();
            stack.add(root);
            Node cur=null;
            while (!stack.isEmpty()){
                cur=stack.pop();
                stack1.push(cur);
                if (cur.left!=null){
                    stack.push(cur.left);
                }
                if (cur.right!=null){
                    stack.push(cur.right);
                }
            }
            while (!stack1.isEmpty()){
                System.out.print(stack1.pop().value+" ");
            }
        }
        System.out.println();
    }

    public static void main(String[] args) {
        Node head = new Node(5);
        head.left = new Node(3);
        head.right = new Node(8);
        head.left.left = new Node(2);
        head.left.right = new Node(4);
        head.left.left.left = new Node(1);
        head.right.left = new Node(7);
        head.right.left.left = new Node(6);
        head.right.right = new Node(10);
        head.right.right.left = new Node(9);
        head.right.right.right = new Node(11);

        // recursive
        System.out.println("==============recursive==============");
        System.out.print("pre-order: ");
        preOrderRecur(head);
        System.out.println();
        System.out.print("in-order: ");
        inOrderRecur(head);
        System.out.println();
        System.out.print("pos-order: ");
        posOrderRecur(head);
        System.out.println();

        // unrecursive
        System.out.println("============unrecursive=============");
        preOrderUnRecur(head);
        inOrderUnRecur(head);
        posOrderUnRecur(head);
    }
}