二叉树获取每个级别的所有节点

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

from collections import deque

def get_nodes_by_level(root):
    if not root:
        return []

    result = []
    queue = deque([root])

    while queue:
        level_nodes = []
        level_size = len(queue)

        for _ in range(level_size):
            node = queue.popleft()
            level_nodes.append(node.val)

            if node.left:
                queue.append(node.left)
            if node.right:
                queue.append(node.right)

        result.append(level_nodes)

    return result

# 构造一个二叉树
#       1
#      / \
#     2   3
#    / \   \
#   4   5   6
root = TreeNode(1)
root.left = TreeNode(2)
root.right = TreeNode(3)
root.left.left = TreeNode(4)
root.left.right = TreeNode(5)
root.right.right = TreeNode(6)

# 获取每个级别的所有节点
result = get_nodes_by_level(root)
print(result)

[[1], [2, 3], [4, 5, 6]]