LeetCode OJ 116. Populating Next Right Pointers in Each Node
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
对于这个题目我们可以很方便的采用层序遍历来解决,每次遍历一层把下一层的节点依次连接起来。由于每一层相当于形成了一个链表,树的最左边的节点就是每一层的起始节点。我们遍历这个链表,把链表中每一个节点的左右节点相连,然后把链表中相邻节点的左孩子和右孩子相连即可。
代码如下:
1 /** 2 * Definition for binary tree with next pointer. 3 * public class TreeLinkNode { 4 * int val; 5 * TreeLinkNode left, right, next; 6 * TreeLinkNode(int x) { val = x; } 7 * } 8 */ 9 public class Solution { 10 public void connect(TreeLinkNode root) { 11 if(root==null) return; 12 TreeLinkNode temp = root; 13 if(temp.left!=null){ 14 while(temp!=null){ //遍历一层 15 temp.left.next = temp.right; 16 if(temp.next!=null){ 17 temp.right.next = temp.next.left; 18 } 19 else{ 20 temp.right.next = null; 21 } 22 temp = temp.next; 23 } 24 connect(root.left); //遍历下一层 25 } 26 return; 27 } 28 }