遍历二叉树

就是遍历二叉树，递归非递归

package my_basic.class_4;

import java.util.Stack;

public class Code_01_PreInPost {
    // 先序 中序 后序遍历二叉树
    //递归 和非递归
    public static class Node {
        int value;
        Node parent;
        Node left;
        Node right;
        public Node(int value) {
            super();
            this.value = value;
        }
    }

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

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

    public static void postOrderRecur(Node head) {
        if (head == null) {
            return;
        }
        postOrderRecur(head.left);
        postOrderRecur(head.right);
        System.out.print(head.value + " ");
    }
    //中左右
    public static void preOrderUnRecur(Node head) {
        Stack<Node> stack = new Stack<Node>();
        stack.add(head);
        while (!stack.isEmpty()) {
            head = stack.pop();
            System.out.print(head.value+" ");
            if (head.right!=null) {
                stack.add(head.right);
            }
            if (head.left!=null) {
                stack.add(head.left);
            }
        }
    }
    //左中右
    public static void inOrderUnRecur(Node head) {
        Stack<Node> stack = new Stack<Node>();
        while(!stack.isEmpty() || head!=null) {
            if (head != null) {
                stack.add(head);
                head = head.left;
            }else {
                head = stack.pop();
                System.out.print(head.value+" ");
                head = head.right;
            }
        }
    }
    //左右中  在先序 中左右 的基础上，改成中右左，然后不输出而是放到另一个栈中
    public static void postOrderUnRecur(Node head) {
        Stack<Node> stack1 = new Stack<Node>();
        Stack<Node> stack2 = new Stack<Node>();
        stack1.add(head);
        while (!stack1.isEmpty()) {
            head = stack1.pop();
//            System.out.print(head.value+" ");
            stack2.add(head);
            if (head.left!=null) {
                stack1.add(head.left);
            }
            if (head.right!=null) {
                stack1.add(head.right);
            }
        }
        while (!stack2.isEmpty()) {
            System.out.print(stack2.pop().value+" ");
        }
    }

    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: ");
        postOrderRecur(head);
        System.out.println();
        System.out.println("==============unrecursive==============");
        System.out.print("pre-order: ");
        preOrderUnRecur(head);
        System.out.println();
        System.out.print("in-order: ");
        inOrderUnRecur(head);
        System.out.println();
        System.out.print("pos-order: ");
        postOrderUnRecur(head);
        

    }

}