sliceutil: helpers for mid-slice insert/delete.

Manipulating the hand, deck, etc. is going to use these operations a lot.
This commit is contained in:
Kistaro Windrider 2023-04-01 18:49:06 -07:00
parent 99e9e35b1d
commit 20561c574c
Signed by: kistaro
SSH Key Fingerprint: SHA256:TBE2ynfmJqsAf0CP6gsflA0q5X5wD5fVKWPsZ7eVUg8
2 changed files with 104 additions and 11 deletions

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@ -31,8 +31,8 @@ func (d *Deck[C]) Len() int {
return len(d.cards)
}
// Insert puts a card at a specific location in the Deck. The card previously
// at that location and all locations after are shifted one card later.
// Insert puts one or more cards at a specific location in the Deck. Cards
// at that location and all locations after are shifted deeper into the deck.
// Negative indexes are counted from the bottom of the deck. BottomOfDeck is
// a sentinel value for the bottommost position; -1 is one card above.
//
@ -44,7 +44,7 @@ func (d *Deck[C]) Len() int {
// WarningTopClamped. Like all warnings, these can be safely ignored and the
// program is in a well-defined state, but you may want to check for them
// if you expect some other behavior.
func (d *Deck[C]) Insert(idx int, card Card[C]) error {
func (d *Deck[C]) Insert(idx int, card ...Card[C]) error {
var errs ErrorCollector
// Calculate actual target index.
switch {
@ -60,14 +60,7 @@ func (d *Deck[C]) Insert(idx int, card Card[C]) error {
idx += d.Len()
}
// remaining case: 0 <= idx <= d.Len(), which is a normal forward insert index.
// Place new card on bottom and "bubble" into position.
// Takes O(N) time. If this turns out to be a problem, implement a more
// efficient data structure.
d.cards = append(d.cards, card)
for i := len(d.cards) - 1; i > idx; i-- {
d.cards[i], d.cards[i-1] = d.cards[i-1], d.cards[i]
}
d.cards = InsertInto(d.cards, idx, card...)
return errs.Emit()
}

100
cardsim/sliceutil.go Normal file
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@ -0,0 +1,100 @@
package cardsim
import (
"fmt"
)
// InsertInto inserts one or more items into a slice at an arbitrary index.
// Items already in the slice past the target position move to later positons.
//
// Like `append`, this may move the underlying array and it produces a new
// slice header (under the hood, it uses `append`). It returns the new slice
// (the original is in an undefined state and should no longer be used).
//
// If loc is negative or more than one past the end of T, Insert panics.
func InsertInto[T any](slice []T, loc int, elements ...T) []T {
if loc < 0 || loc > len(slice) {
panic(fmt.Sprintf("can't Insert at location %d in %d-element slice", loc, len(slice)))
}
// is this a no-op?
if len(elements) == 0 {
return slice
}
// is this just an append?
if loc == len(slice) {
return append(slice, elements...)
}
offset := len(elements)
oldLen := len(slice)
newSize := oldLen + offset
if newSize <= cap(slice) {
// We can reslice in place.
slice = slice[:newSize]
// Scoot trailing to their new positions.
copy(slice[loc+offset:], slice[loc:oldLen])
// Insert the new elements.
copy(slice[loc:], elements)
return slice
}
// Reallocate. Do the normal thing of doubling the size as a minimum
// when increasing space for a dynamic array; this amortizes the
// cost of repeatedly reallocating and moving the slice.
newCap := cap(slice) * 2
if newCap < newSize {
newCap = newSize
}
newSlice := make([]T, newSize, newCap)
if loc > 0 {
copy(newSlice, slice[0:loc])
}
copy(newSlice[loc:], elements)
copy(newSlice[loc+offset:], slice[loc:])
return newSlice
}
// DeleteFrom deletes an item from a slice at an arbitrary index. Items after it
// scoot up to close the gap. This returns the modified slice (like Append).
//
// If the provided location is not a valid location in the slice, this panics.
func DeleteFrom[T any](slice []T, loc int) []T {
return DeleteNFrom(slice, loc, 1)
}
// DeleteNFrom deletes N items from a slice at an arbitrary index. Items after
// it scoot up to close the gap. This returns the modified slice (like Append).
//
// If the range of items that would be deleted is not entirely valid within the
// slice, this panics.
func DeleteNFrom[T any](slice []T, loc, n int) []T {
if loc < 0 || loc+n > len(slice) {
panic(fmt.Sprintf("can't delete %d elements from a %d-element slice at location %d", n, len(slice), loc))
}
// Easy cases.
if n == 0 {
return slice
}
if loc == 0 {
return slice[n:]
}
if loc+n == len(slice) {
return slice[0:loc]
}
// Is it shorter to move up or move down?
if len(slice)-loc-n > loc {
// Move forward -- the end is big.
copy(slice[n:], slice[:loc])
return slice[n:]
}
// Move backward -- the beginnng is big or they're the same size
// (and moving backwards preserves more usable append capacity later).
copy(slice[loc:], slice[loc+n:])
return slice[:len(slice)-n]
}