二叉树遍历

请递归，非递归方式分别前序遍历，中序遍历，后续遍历二叉树

public class TraversalTree{
    public static class Node {
        public int value;
        public Node left;
        public Node right;
    }

// 前序递归
public static void preOrderRecur(Node head) {
    if (head == null) {
        return;
    }

    System.out.print(head.value + " ");
    preOrderRecur(head.left);
    preOrderRecur(head.right);
}

//中序递归
public static void inOrderRecur(Node head) {
    if (head == null) {
        return;
    }

    inOrderRecur(head.left);
    System.out.println(head.value + " ");
    inOrderRecur(head.right);
}

//后序递归
public static void posOrderRecur(Node head) {
      if (head == null) {
          return;
      }
      posOrderRecur(head.left);
      System.out.println(head.value + " ");
      posOrderRecur(head.right);
  }
  

//非递归前序遍历   
public static void preOrderUnRecur(Node head) {
        if (head == null) {
            return;
        }
    
        Stack<Node> stack = new Stack<Node>();
        stack.push(head);
        while(!stack.isEmpty()) {
            Node node = stack.pop();
            System.out.println(node.value + " ");
            if (node.left != null) {
                node.push(node.left);
            }
    
            if (node.right != null) {
                node.push(node.right);
            }
        }
    }

//非递归中序遍历   
public static void inOrderUnRecur(Node head) {
        if (head == null) {
            return;
        }
    
        Stack<Node> stack = new Stack<Node>();
        while(!stack.isEmpty() || head != null) {
            if (head != null) {
                stack.push(head);
                head = head.left;
            } else {
                head = stack.pop();
                System.out.println(head.value + " ");
                head = head.right;
            }
        }   
    }

//非递归后续遍历
public static void postOrderUnRecur(Node head) {
       if (head != null) {
           Stack<Node> s1 = new Stack<Node>();
           Stack<Node> s2 = new Stack<Node>();
           s1.push(head);
           while(!s1.isEmpty()) {
               head = s1.pop();
               s2.push(head);
               if (head.left != null) {
                   s1.push(head.left);
               } 
               if (head.right != null) {
                   s1.push(head.right);
               }
           }
   
           while(!s2.isEmpty()) {
               System.out.println(s2.pop().value + " ");
           }
       }
   }
}