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leetcode解题-binary tree level order traversal

admin 11月 11, 2020 0

描述

Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).

For example:
Given binary tree {3,9,20,#,#,15,7},
3
/
9 20
/
15 7
return its level order traversal as:
[
[3],
[9,20],
[15,7]
]

分析

广度优先遍历，用队列实现。

代码

Python

from collections import deque, OrderedDict



class (object):
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None


class Solution(object):
    def levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        queue = deque()
        d = OrderedDict()
        if not root:
            return []
        queue.append((root, 0))
        while queue:
            cur, idx = queue.popleft()
            d.setdefault(idx, []).append(cur.val)
            if cur.left:
                queue.append((cur.left, idx + 1))
            if cur.right:
                queue.append((cur.right, idx + 1))
        return d.values()