题目链接

层序遍历

/*
// 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) {
        Deque<Node> queue = new LinkedList<Node>();
        if(root != null){
            queue.offer(root);
        }
        while(!queue.isEmpty()){
            int size = queue.size();
            for(int i = 0; i < size; i++){
                Node node = queue.poll();
                if(node.left != null){
                    queue.offer(node.left);
                }
                if(node.right != null){
                    queue.offer(node.right);
                }
                 if(i == size - 1){
                    node.next = null;
                }else{
                    node.next = queue.getFirst();
                }
            }
        }
        return root;
    }
}