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posOrderArr.go
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/
posOrderArr.go
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package traversal
import (
"github.com/NewbMiao/algorithm-go/kit/btree"
)
// BST post order arr check.
func IsPosOrderArr(arr []int) bool {
if len(arr) == 0 {
return false
}
return isPosOrder(arr, 0, len(arr)-1)
}
func isPosOrder(arr []int, start, end int) bool {
if start == end { // self no need cmp
return true
}
less := -1
more := end
for i := start; i < end; i++ {
if arr[end] > arr[i] {
less = i
} else if more == end {
more = i
}
}
if less == -1 || more == end {
return isPosOrder(arr, start, end-1)
}
if less != more-1 { // no asc order
return false
}
return isPosOrder(arr, start, less) && isPosOrder(arr, more, end-1)
}
func PosOrderArrToBST(arr []int) (bt *btree.Node) {
if len(arr) == 0 {
return
}
return posToBST(arr, 0, len(arr)-1)
}
func posToBST(arr []int, start, end int) (bt *btree.Node) {
if start > end { // should finish current loop
return
}
less := -1
more := end
head := &btree.Node{Value: arr[end]}
for i := start; i < end; i++ {
if arr[end] > arr[i] {
less = i
} else if more == end {
more = i
}
}
head.Left = posToBST(arr, start, less)
head.Right = posToBST(arr, more, end-1)
return head
}