return s[:len(s):len(s)]
}
-// Rotation algorithm explanation:
-//
-// rotate left by 2
-// start with
-// 0123456789
-// split up like this
-// 01 234567 89
-// swap first 2 and last 2
-// 89 234567 01
-// join first parts
-// 89234567 01
-// recursively rotate first left part by 2
-// 23456789 01
-// join at the end
-// 2345678901
-//
-// rotate left by 8
-// start with
-// 0123456789
-// split up like this
-// 01 234567 89
-// swap first 2 and last 2
-// 89 234567 01
-// join last parts
-// 89 23456701
-// recursively rotate second part left by 6
-// 89 01234567
-// join at the end
-// 8901234567
-
// TODO: There are other rotate algorithms.
-// This algorithm has the desirable property that it moves each element exactly twice.
-// The triple-reverse algorithm is simpler and more cache friendly, but takes more writes.
+// This algorithm has the desirable property that it moves each element at most twice.
// The follow-cycles algorithm can be 1-write but it is not very cache friendly.
-// rotateLeft rotates b left by n spaces.
+// rotateLeft rotates s left by r spaces.
// s_final[i] = s_orig[i+r], wrapping around.
func rotateLeft[E any](s []E, r int) {
- for r != 0 && r != len(s) {
- if r*2 <= len(s) {
- swap(s[:r], s[len(s)-r:])
- s = s[:len(s)-r]
- } else {
- swap(s[:len(s)-r], s[r:])
- s, r = s[len(s)-r:], r*2-len(s)
- }
- }
+ Reverse(s[:r])
+ Reverse(s[r:])
+ Reverse(s)
}
func rotateRight[E any](s []E, r int) {
rotateLeft(s, len(s)-r)
}
-// swap swaps the contents of x and y. x and y must be equal length and disjoint.
-func swap[E any](x, y []E) {
- for i := 0; i < len(x); i++ {
- x[i], y[i] = y[i], x[i]
- }
-}
-
// overlaps reports whether the memory ranges a[0:len(a)] and b[0:len(b)] overlap.
func overlaps[E any](a, b []E) bool {
if len(a) == 0 || len(b) == 0 {