Python implements binary tree level traversal (breadth-first traversal)

1. Python implements binary tree level traversal

1. Leetcode topic link

102. Level order traversal of binary tree

2. Realize

Mainly use the deque queue to achieve:

class Solution:
    """二叉树层序遍历迭代解法"""

    def levelOrder(self, root: TreeNode) -> List[List[int]]:
        results = []
        if not root:
            return results

        from collections import deque
        que = deque([root])

        while que:
            size = len(que)
            result = []
            for _ in range(size):
                cur = que.popleft()
                result.append(cur.val)
                if cur.left:
                    que.append(cur.left)
                if cur.right:
                    que.append(cur.right)
            results.append(result)

        return results