Populating Next Right Pointers in Each Node

题目地址:https://oj.leetcode.com/problems/populating-next-right-pointers-in-each-node/;

题目描述:

Given a binary tree

struct TreeLinkNode {
TreeLinkNode *left;
TreeLinkNode *right;
TreeLinkNode *next;
}

Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to

NULL

.

Initially, all next pointers are set to

NULL

.

Note:

You may only use constant extra space.
You may assume that it is a perfect binary tree (ie, all leaves are at the same level, and every parent has two children).

For example,

Given the following perfect binary tree,

1
/  \
2    3
/ \  / \
4  5  6  7

After calling your function, the tree should look like:

1 -> NULL
/  \
2 -> 3 -> NULL
/ \  / \
4->5->6->7 -> NULL

解题思路:这道题可以用层次遍历二叉树来解答。在二叉树的每一层的节点个数是2的i次方，(i>=0&&i<=树的层次)，因此需要在设置一个变量来保存每一层的节点个数，当每一层的节点访问完之后，可得到每一层的最后节点，然后对最后一个节点操作即可。