LeetCode——Populating Next Right Pointers in Each Node II

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

原题链接：https://oj.leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/
题目：前一题的继续，如果给定的是任意的二叉树，前题的代码还能用吗？

思路：显然，前一题不能用了。只好用层序遍历。

public void connect(TreeLinkNode root) {
if(root == null)
return;
TreeLinkNode parent = root,pre,next;
while(parent != null){
pre = null;
next = null;
while(parent != null){
if(next == null)
next = (parent.left == null) ? parent.right : parent.left;
if(parent.left != null){
if(pre != null){
pre.next = parent.left;
pre = pre.next;
}else
pre = parent.left;
}
if(parent.right != null){
if(pre != null){
pre.next = parent.right;
pre = pre.next;
}else
pre = parent.right;
}
parent = parent.next;
}
parent = next;
}
}