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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],
3
/ \
9 20
/ \
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
}