I'm writing a function that returns the vertical order traversal of a binary tree's node values. (ie, from top to bottom, column by column). Here's an example of expected input and output:
Input: [3,9,8,4,0,1,7,null,null,null,2,5] (0's right child is 2 and 1's left child is 5)
3
/\
/ \
9 8
/\ /\
/ \/ \
4 01 7
/\
/ \
5 2
Output:
[
[4],
[9,5],
[3,0,1],
[8,2],
[7]
]
My function outputs everything as expected except for [8,2]—I'm getting [2,8] instead:
[[4] [9 5] [3 0 1] [2 8] [7]]
This is what my function looks like:
func verticalOrder(root *TreeNode) [][]int {
if root == nil {
return [][]int{}
}
var (
hd int
m map[int][]int
vals [][]int
min int
max int
traverse func(t *TreeNode, hd int, m map[int][]int)
)
m = make(map[int][]int)
min = 0
max = 0
traverse = func(t *TreeNode, hd int, m map[int][]int) {
if t == nil {
return
}
m[hd] = append(m[hd], t.Val)
if max < hd {
max = hd
}
if min > hd {
min = hd
}
traverse(t.Left, hd-1, m)
traverse(t.Right, hd+1, m)
}
traverse(root, hd, m)
for i := min; i <= max; i++ {
vals = append(vals, m[i])
}
return vals
}
Essentially, I'm using a hash map to keep track of nodes with the same horizontal distance, and appending them to an array. What I'm trying to figure out is how come my output works properly with 9 and 5 but not with 8 and 2? Any feedback is much appreciated!
Steps to reproduce
Run the code below. You'll get an output of [[4] [9 5] [3 0 1] [2 8] [7]]; the output should be [[4] [9 5] [3 0 1] [8 2] [7]]. The thing that's tripping me up is [9 5] is appending in the correct, vertical order, whereas [2 8] is not despite being similar, so I'm not too sure where to go from here.
package main
import "fmt"
// TreeNode is a binary tree node.
type TreeNode struct {
Val int
Left *TreeNode
Right *TreeNode
}
func verticalOrder(root *TreeNode) [][]int {
if root == nil {
return [][]int{}
}
var (
hd int
m map[int][]int
vals [][]int
min int
max int
traverse func(t *TreeNode, hd int, m map[int][]int)
)
m = make(map[int][]int)
min = 0
max = 0
traverse = func(t *TreeNode, hd int, m map[int][]int) {
if t == nil {
return
}
m[hd] = append(m[hd], t.Val)
if max < hd {
max = hd
}
if min > hd {
min = hd
}
traverse(t.Left, hd-1, m)
traverse(t.Right, hd+1, m)
}
traverse(root, hd, m)
for i := min; i <= max; i++ {
vals = append(vals, m[i])
}
return vals
}
func main() {
root := &TreeNode{
Val: 3,
Left: &TreeNode{
Val: 9,
Left: &TreeNode{
Val: 4,
Left: nil,
Right: nil,
},
Right: &TreeNode{
Val: 0,
Left: nil,
Right: &TreeNode{
Val: 2,
Left: nil,
Right: nil,
},
},
},
Right: &TreeNode{
Val: 8,
Left: &TreeNode{
Val: 1,
Left: &TreeNode{
Val: 5,
Left: nil,
Right: nil,
},
Right: nil,
},
Right: &TreeNode{
Val: 7,
Left: nil,
Right: nil,
},
},
}
fmt.Println(verticalOrder(root))
}
