填充每個節點的下一個右側節點指標 II

輸入：root = [1,2,3,4,5,null,7]
輸出：[1,#,2,3,#,4,5,7,#]
解釋：給定二叉樹如圖 A 所示，你的函式應該填充它的每個 next 指標，以指向其下一個右側節點，如圖 B 所示。

來源：力扣（LeetCode）
連結：https://leetcode-cn.com/problems/populating-next-right-pointers-in-each-node-ii
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/*
// 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<Node>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            int n = queue.size();
            Node last = null;
            for (int i = 1; i <= n; ++i) {
                Node f = queue.poll();
                if (f.left != null) {
                    queue.offer(f.left);
                }
                if (f.right != null) {
                    queue.offer(f.right);
                }
                if (i != 1) {
                    last.next = f;
                }
                last = f;
            }
        }
        return root;
    }
}