题解 | #求二叉树的层序遍历#

class Solution:
    def levelOrder(self , root: TreeNode) -> List[List[int]]:
        if not root:return []
        ans,que = [],[root]
        # 遍历每一层
        while que:
            res = []
            # 遍历当前层每个结点
            for _ in range(len(que)):
                node = que[0]
                res.append(node.val)
                que.pop(0)
                if node.left :que.append(node.left)
                if node.right :que.append(node.right)
            ans.append(res)
        return ans