LeetCode 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

Runtime: 1
ms  beats 34.25% of java submissions.

public void connect(TreeLinkNode root) {
if (root == null || root.left == null) return;
root.left.next = root.right;
if (root.next != null) {
root.right.next = root.next.left;
} else root.right.next = null;
connect(root.left);
connect(root.right);
}