117. 填充每个节点的下一个右侧节点指针 II

BFS模板的应用

总结的DFS、BFS模板参考：https://www.cnblogs.com/panweiwei/p/13065661.html

class Solution(object):
    def connect(self, root):
        """
        :type root: Node
        :rtype: Node
        """
        if not root:
            return root
        queue = [root]
        while queue:
            l = len(queue)
            for i in range(l):
                node = queue.pop(0)
                if i < l - 1:
                    node.next = queue[0]
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
        return root