LeetCode: Next Right Pointer in Each Node (Binary Tree)

// 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

/**
 * Definition for binary tree with next pointer.
 * public class TreeLinkNode {
 *     int val;
 *     TreeLinkNode left, right, next;
 *     TreeLinkNode(int x) { val = x; }
 * }
 */
public class PopulatingNextRightPointersInEachNode {
    public void connect(TreeLinkNode root) {
        if(root == null) {
            return;
        }
     
        Queue<TreeLinkNode> queue = new LinkedList<TreeLinkNode>();
     
        queue.add(root);
     
        while(!queue.isEmpty()) {
            Queue<TreeLinkNode> currentLevel = new LinkedList<TreeLinkNode>();
         
            TreeLinkNode temp = null;
         
            while(!queue.isEmpty()) {
                TreeLinkNode current = queue.remove();
                current.next = temp;
                temp = current;
             
             
                if(current.right != null) {
                    currentLevel.add(current.right);
                }
             
                if(current.left!= null) {
                    currentLevel.add(current.left);
                }
            }
         
            queue = currentLevel;
        }
    }
}