107. Binary Tree Level Order Traversal II

题目

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

For Example:

Given binary tree [3,9,20,null,null,15,7],

return its bottom-up level order traversal as:


[
  [15,7],
  [9,20],
  [3]
]

题目大意

按层序从下到上遍历一颗树。

解题思路

用一个队列即可实现。

代码


package leetcode

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func levelOrderBottom(root *TreeNode) [][]int {
	tmp := levelOrder(root)
	res := [][]int{}
	for i := len(tmp) - 1; i >= 0; i-- {
		res = append(res, tmp[i])
	}
	return res
}