[Lintcode]69. Binary Tree Level Order Traversal/[Leetcode]102. Binary Tree Level Order Traversal

69. Binary Tree Level Order Traversal/102. Binary Tree Level Order Traversal

• 本题难度: Easy/Medium
• Topic: Binary Tree

Description

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

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]
]
Challenge
Challenge 1: Using only 1 queue to implement it.

Challenge 2: Use BFS algorithm to do it.

我的代码

"""
Definition of TreeNode:
class TreeNode:
    def __init__(self, val):
        self.val = val
        self.left, self.right = None, None
"""

class Solution:
    """
    @param root: A Tree
    @return: Level order a list of lists of integer
    """
    def high(self,root,res,h):
        if root is None:
            return res
        if len(res)<h:
            res.append([root.val])
        else:
            res[h-1].append(root.val)
        res = self.high(root.left,res,h+1)
        res = self.high(root.right,res,h+1)
        return res
    
    def levelOrder(self, root):
        # write your code here
        if root is None:
            return []
        return self.high(root,[],1)

思路
深度优先遍历，根据深度确定所在的层数