Tree - 103. Binary Tree Zigzag Level Order Traversal
103. Binary Tree Zigzag Level Order Traversal
Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between).
For example:
Given binary tree [3,9,20,null,null,15,7]
,
3
/ \
9 20
/ \
15 7
return its zigzag level order traversal as:
[
[3],
[20,9],
[15,7]
]
思路:
简单的层序遍历实现题,思想是bfs,只是在输出结果上用做z字序。
代码:
go:
/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func zigzagLevelOrder(root *TreeNode) [][]int {
var (
res [][]int
level []int
curQ = []*TreeNode{root}
nextQ []*TreeNode
reverse = false
)
if root == nil {
return res
}
for len(curQ) != 0 {
for len(curQ) != 0 {
var cur *TreeNode
cur = curQ[0]
curQ = curQ[1:]
level = append(level, cur.Val)
if cur.Left != nil {
nextQ = append(nextQ, cur.Left)
}
if cur.Right != nil {
nextQ = append(nextQ, cur.Right)
}
}
if reverse {
var out []int
for i := len(level) -1; i >= 0; i-- {
out = append(out, level[i])
}
level = out
}
res = append(res, level)
level= nil
curQ = nextQ
nextQ = nil
if reverse {
reverse = false
} else {
reverse = true
}
}
return res
}