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层次遍历求解，程序如下所示：/**
* Definition for binary tree with next pointer.
* public class TreeLinkNode {
* int val;
* TreeLinkNode left, right, next;
* TreeLinkNode(int x) { val = x; }
* }
*/
public class Solution {
public void connect(TreeLinkNode root) {
if (root == null){
return ;
}
ArrayDeque<TreeLinkNode> que = new ArrayDeque<>();
que.offer(root);
int size = 0;
while (!que.isEmpty()){
size = que.size();
TreeLinkNode tmp;
TreeLinkNode pre = null;
for (int i = 0; i < size; ++ i){
tmp = que.poll();
if (tmp.left != null){
que.offer(tmp.left);
}
if (tmp.right != null){
que.offer(tmp.right);
}
if (pre != null){
pre.next = tmp;
}
pre = tmp;
}
}
}
}