117. Populating Next Right Pointers in Each Node II.java

/*
// Definition for a Node.
class Node {
    public int val;
    public Node left;
    public Node right;
    public Node next;

    public Node() {}
    
    public Node(int _val) {
        val = _val;
    }

    public Node(int _val, Node _left, Node _right, Node _next) {
        val = _val;
        left = _left;
        right = _right;
        next = _next;
    }
};
*/

class Solution {
    public Node connect(Node root) {
        if(root == null)
            return root;
        
        LinkedList<Node> q = new LinkedList<>();
        q.add(root);
        
        while(q.size() > 0)
        {
            int size = q.size();
            Node prev = q.getFirst();
            while(size-- > 0)
            {
                Node rem = q.removeFirst();
                if(rem != prev)
                {
                    prev.next = rem;
                    prev = rem;
                }
                if(rem.left != null)
                    q.add(rem.left);
                if(rem.right != null)
                    q.add(rem.right);
            }
        }
        
        return root;
    }
}