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

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Java Code:

/**
* 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 ;
}

TreeLinkNode[] lastNode = {null};
listConnect(root, lastNode);
connect(lastNode[0]);
}

public void listConnect(TreeLinkNode root, TreeLinkNode[] lastNode) {
if (root == null) {
return ;
}

listConnect(root.next, lastNode);
if(root.right != null) {
root.right.next = lastNode[0];
}
if(root.left != null) {
root.left.next = root.right;
lastNode[0] = root.left;
}
}
}