leetcode/Problem116/Solution.java at master · gorthitk/leetcode · GitHub

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class Solution {
    public Node connect(Node root) {
        if (root == null) {
            return root;
        }

        Queue<Node> queue = new LinkedList<>();
        queue.add(root);

        while(!queue.isEmpty()) {
            int sz = queue.size();
            Node prev = null;
            while(sz-- > 0) {
                Node curr = queue.poll();
                if (prev != null) {
                    prev.next = curr;
                }
                prev = curr;

                if (curr.left != null) {
                    queue.add(curr.left);
                }

                if (curr.right != null) {
                    queue.add(curr.right);
                }
            }
        }


        return root;
    }
}