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intervaltree.go
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intervaltree.go
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package intervaltree
import (
"time"
"errors"
// "fmt"
)
// wishlist
// polymorphic intervals with an interface and a method to compare them
// a payload within each interval
// AVL tree or red black tree insertion/deletion instead of BST
/*
Base IntervalTree class.
Entry point for the tree (instead of just holding a pointer to root).
Use *IntervalTree Receiver Type to avoid copying
*/
type IntervalTree struct {
root *IntervalTreeNode
}
func NewIntervalTree() *IntervalTree {
// constructor: create tree (empty)
return &IntervalTree{nil}
}
func (tree *IntervalTree) Empty() bool {
// Empty: returns boolean if tree is empty
return tree.root == nil
}
func (tree *IntervalTree) Insert(i Interval) {
// Insert: inserts an interval
if tree.Empty() {
tree.root = newIntervalTreeNode(i)
} else {
tree.root.insert(i)
}
}
func (tree *IntervalTree) FindOverlap(i Interval) []Interval {
// FindOverlap: find all intervals overlapping with an interval
if tree.Empty() {
var overlaps []Interval
return overlaps
} else {
overlaps := tree.root.findOverlap(i)
return overlaps
}
}
func (tree *IntervalTree) Overlaps(i Interval) bool {
// Overlaps: check if any interval in tree overlaps an interval
if tree.Empty() {
return false
} else {
return tree.root.overlaps(i)
}
}
/*
A node in the interval tree, useful for balanced tree insertion
without having to contaminate interval class.
*/
type IntervalTreeNode struct {
i Interval
subTreeMax time.Time
left *IntervalTreeNode
right *IntervalTreeNode
}
func newIntervalTreeNode(i Interval) *IntervalTreeNode {
// TODO: return error if i is nil
node := new(IntervalTreeNode)
node.i = i
node.subTreeMax = i.End()
return node
}
func (node *IntervalTreeNode) insert(i Interval) *IntervalTreeNode {
start := node.i.Start()
if i.End().Before(start) {
if node.left == nil {
node.left = newIntervalTreeNode(i)
} else {
node.left.insert(i)
}
} else {
if node.right == nil {
node.right = newIntervalTreeNode(i)
} else {
node.right.insert(i)
}
}
// update max for searching later
if node.subTreeMax.Before(i.End()) {
node.subTreeMax = i.End()
}
return node
}
func (node *IntervalTreeNode) findOverlap(i Interval) []Interval {
// TODO: be more efficient with searching, this is just going through every single node
var overlaps []Interval
if Overlaps(node.i, i) {
overlaps = append(overlaps, node.i)
}
if node.left != nil {
overlaps = append(overlaps, node.left.findOverlap(i)...)
}
if node.right != nil {
overlaps = append(overlaps, node.right.findOverlap(i)...)
}
return overlaps
}
func (node *IntervalTreeNode) overlaps(i Interval) bool {
// TODO: be more efficient searching
if Overlaps(node.i, i) {
return true
} else if node.left != nil && node.left.overlaps(i) {
return true
} else if node.right != nil && node.right.overlaps(i) {
return true
} else {
return false
}
}
/*
Start and End times only.
Pass these by value instead of pointer because don't want any
unexpected modifications (would destroy integrity of tree) and its safer.
TODO: polymorphic intervals
Immutable start and end so that intervals are always valid.
*/
type Interval struct {
start time.Time
end time.Time
// Payload PayLoad
}
func NewInterval(start time.Time, end time.Time) (Interval, error) {
var i Interval
if start.After(end) {
return i, errors.New("Interval::NewInterval end cannot come after start.")
} else if start.Equal(end) {
return i, errors.New("Interval::NewInterval start cannot equal end.")
} else {
return Interval{start, end}, nil
}
}
func (i Interval) Start() time.Time {
return i.start
}
func (i Interval) End() time.Time {
return i.end
}
// start_datetime1 <= end_datetime2 and end_datetime1 >= start_datetime2
func Overlaps(i1 Interval, i2 Interval) bool {
return i1.Start().Before(i2.End()) && i1.End().After(i2.Start())
}