# 0116. Populating Next Right Pointers in Each Node

<https://leetcode.com/problems/populating-next-right-pointers-in-each-node>

## Description

You are given a **perfect binary tree** where all leaves are on the same level, and every parent has two children. The binary tree has the following definition:

```
struct Node {
  int val;
  Node *left;
  Node *right;
  Node *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`.

**Example 1:**

![](https://assets.leetcode.com/uploads/2019/02/14/116_sample.png)

```
**Input:** root = [1,2,3,4,5,6,7]
**Output:** [1,#,2,3,#,4,5,6,7,#]
**Explanation:** Given the above perfect binary tree (Figure A), your function should populate each next pointer to point to its next right node, just like in Figure B. The serialized output is in level order as connected by the next pointers, with '#' signifying the end of each level.
```

**Example 2:**

```
**Input:** root = []
**Output:** []
```

**Constraints:**

* The number of nodes in the tree is in the range `[0, 212 - 1]`.
* `-1000 <= Node.val <= 1000`

**Follow-up:**

* You may only use constant extra space.
* The recursive approach is fine. You may assume implicit stack space does not count as extra space for this problem.

## ac1: iterative

```java
public class Solution {
    public void connect(TreeLinkNode root) {
        //edge case
        if (root == null) return;

        // record: leftParent, currParent, curr
        TreeLinkNode leftParent, currParent, curr;
        TreeLinkNode dummy = new TreeLinkNode(0);
        leftParent = root;
        while (leftParent.left != null) {
            currParent = leftParent;
            curr = dummy;
            while (currParent != null) {
                currParent.left.next = currParent.right;
                curr.next = currParent.left;
                curr = currParent.right;
                currParent = currParent.next;
            }
            leftParent = leftParent.left;
        }
    }
}
```

## ac2: recursive

```java
// Jesus... what a smart solution, beautiful...
public class Solution {
    public void connect(TreeLinkNode root) {
        //edge case
        if (root == null || root.left == null) return;

        root.left.next = root.right;
        if (root.next != null) {
            root.right.next = root.next.left;
        }

        connect(root.left);
        connect(root.right);
    }
}
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://jaywin.gitbook.io/leetcode/solutions/0116-populating-next-right-pointers-in-each-node.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.