题目
给定一个二叉树,返回其按层次遍历的节点值。(即逐层地,从左到右访问所有节点)。
例如:
给定二叉树: [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
返回其层次遍历结果:
[
[3],
[9,20],
[15,7]
]
方案一(广度优先搜索)
/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func levelOrder(root *TreeNode) [][]int {
if root == nil {
return [][]int{}
}
ret := [][]int{}
queue := []*TreeNode{root}
depth := -1
for len(queue) > 0 {
depth += 1
length := len(queue)
ret = append(ret, make([]int, 0, length))
for i := 0; i < length; i++ {
node := queue[0]
queue = queue[1:]
ret[depth] = append(ret[depth], node.Val)
if node.Left != nil {queue = append(queue, node.Left)}
if node.Right != nil {queue = append(queue, node.Right)}
}
}
return ret
}
原文
https://leetcode-cn.com/explore/learn/card/data-structure-binary-tree/2/traverse-a-tree/9/