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