LeetCode 之 Populating Next Right Pointers in Each Node II

原题：

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,

这个题是学渣遇到最无奈的一个题。。。。竟然用了1的代码没改就过了。。。。尼玛，莫非是做1的时候想的太多？

Populating Next Right Pointers in Each Node

我看了一下1和2的区别就是2不是完全二叉树。。。。然后其实就是需要判断一下左子树是否为空，若为空，不入栈