/*
 * @lc app=leetcode.cn id=116 lang=java
 *
 * [116] 填充每个节点的下一个右侧节点指针
 *
 * https://leetcode-cn.com/problems/populating-next-right-pointers-in-each-node/description/
 *
 * algorithms
 * Medium (59.25%)
 * Likes:    191
 * Dislikes: 0
 * Total Accepted:    37.4K
 * Total Submissions: 61.8K
 * Testcase Example:  '[1,2,3,4,5,6,7]'
 *
 * 给定一个完美二叉树，其所有叶子节点都在同一层，每个父节点都有两个子节点。二叉树定义如下：
 *
 * struct Node {
 * ⁠ int val;
 * ⁠ Node *left;
 * ⁠ Node *right;
 * ⁠ Node *next;
 * }
 *
 * 填充它的每个 next 指针，让这个指针指向其下一个右侧节点。如果找不到下一个右侧节点，则将 next 指针设置为 NULL。
 *
 * 初始状态下，所有 next 指针都被设置为 NULL。
 *
 *
 *
 * 示例：
 *
 *
 *
 *
 * 输入：{"$id":"1","left":{"$id":"2","left":{"$id":"3","left":null,"next":null,"right":null,"val":4},"next":null,"right":{"$id":"4","left":null,"next":null,"right":null,"val":5},"val":2},"next":null,"right":{"$id":"5","left":{"$id":"6","left":null,"next":null,"right":null,"val":6},"next":null,"right":{"$id":"7","left":null,"next":null,"right":null,"val":7},"val":3},"val":1}
 *
 *
 * 输出：{"$id":"1","left":{"$id":"2","left":{"$id":"3","left":null,"next":{"$id":"4","left":null,"next":{"$id":"5","left":null,"next":{"$id":"6","left":null,"next":null,"right":null,"val":7},"right":null,"val":6},"right":null,"val":5},"right":null,"val":4},"next":{"$id":"7","left":{"$ref":"5"},"next":null,"right":{"$ref":"6"},"val":3},"right":{"$ref":"4"},"val":2},"next":null,"right":{"$ref":"7"},"val":1}
 *
 * 解释：给定二叉树如图 A 所示，你的函数应该填充它的每个 next 指针，以指向其下一个右侧节点，如图 B 所示。
 *
 *
 *
 *
 * 提示：
 *
 *
 * 你只能使用常量级额外空间。
 * 使用递归解题也符合要求，本题中递归程序占用的栈空间不算做额外的空间复杂度。
 *
 *
 */

// @lc code=start
/*
// 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 null;
    }

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

    while (!queue.isEmpty()) {
      int size = queue.size();
      Node pre = null;
      for (int i = 0; i < size; i++) {
        Node node = queue.poll();
        node.next = pre;
        pre = node;
        if (node.right != null) {
          queue.offer(node.right);
        }
        if (node.left != null) {
          queue.offer(node.left);
        }
      }
    }

    return root;
  }
}
// @lc code=end

