morris遍历的优点在于节省空间，因为不需要递归。

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

        morris(head);
        morris2(head);
    }

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

        public Node(int data){
            this.value = data;
        }
    }

    public static void morris(Node head){
        if(head == null){
            return ;
        }

        Node cur = head;
        Node mostRight = null;
        boolean isRighNull = true;
        while(cur != null){
            System.out.print(cur.value+"  ");
            if(cur.left == null){ // 如果cur没有左孩子,cur向右移动
                cur = cur.right;
            }else{
                    mostRight = cur.left;
                    isRighNull = true;
                    while (mostRight.right != null) {
                        if(mostRight.right == cur){
                            isRighNull = false;
                            break;
                        }
                        mostRight = mostRight.right;
                    }

                    if (isRighNull) {
                        mostRight.right = cur;
                        cur = cur.left;
                    }else{
                        mostRight.right = null;
                        cur = cur.right;
                    }
            }
        }
        System.out.println();
    }

    public static void morris2(Node head){
        if(head == null){
            return ;
        }

        Node cur = head;
        Node mostRight = null;
        while(cur != null){
            System.out.print(cur.value+"  ");
            mostRight = cur.left;
            if(mostRight != null){// 如果cur没有左孩子,cur向右移动
                while (mostRight.right != null && mostRight.right != cur){
                    mostRight = mostRight.right;
                }
                if(mostRight.right == null){
                    mostRight.right = cur;
                    cur = cur.left;
                    continue;
                }else{
                    mostRight.right = null;
                }
            }
                cur = cur.right;
        }
        System.out.println();
    }
}