Leetcode 117. Populating Next Right Pointers in Each Node II

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针对Populating Next Right Pointers in Each Node问题的进阶版本，本文介绍了一种仅使用常数额外空间填充任意二叉树节点的方法，并提供了一个Java实现示例。

Question

Follow up for problem “Populating Next Right Pointers in Each Node”.

What if the given tree could be any binary tree? Would your previous solution still work?

Note:

You may only use constant extra space.
For example,
Given the following binary tree,
1
/ \
2 3
/ \ \
4 5 7
After calling your function, the tree should look like:
1 -> NULL
/ \
2 -> 3 -> NULL
/ \ \
4-> 5 -> 7 -> NULL

Code

 public void connect(TreeLinkNode root) {
        if (root == null) {
            return;
        }

        TreeLinkNode leftEnd = root;

        while (leftEnd != null) {
            TreeLinkNode cur = leftEnd;
            TreeLinkNode dummy = new TreeLinkNode(0);
            TreeLinkNode pre = dummy;
            while (cur != null) {
                if (cur.left != null) {
                    pre.next = cur.left;
                    pre = cur.left;
                }

                if (cur.right != null) {
                    pre.next = cur.right;
                    pre = cur.right;
                }

                cur = cur.next;
            }
            leftEnd = dummy.next;
        }
    }