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114 lines
2.9 KiB
Go
114 lines
2.9 KiB
Go
// Copyright 2022 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package lcs
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// This file defines the abstract sequence over which the LCS algorithm operates.
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// sequences abstracts a pair of sequences, A and B.
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type sequences interface {
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lengths() (int, int) // len(A), len(B)
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commonPrefixLen(ai, aj, bi, bj int) int // len(commonPrefix(A[ai:aj], B[bi:bj]))
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commonSuffixLen(ai, aj, bi, bj int) int // len(commonSuffix(A[ai:aj], B[bi:bj]))
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}
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type stringSeqs struct{ a, b string }
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func (s stringSeqs) lengths() (int, int) { return len(s.a), len(s.b) }
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func (s stringSeqs) commonPrefixLen(ai, aj, bi, bj int) int {
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return commonPrefixLenString(s.a[ai:aj], s.b[bi:bj])
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}
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func (s stringSeqs) commonSuffixLen(ai, aj, bi, bj int) int {
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return commonSuffixLenString(s.a[ai:aj], s.b[bi:bj])
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}
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// The explicit capacity in s[i:j:j] leads to more efficient code.
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type bytesSeqs struct{ a, b []byte }
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func (s bytesSeqs) lengths() (int, int) { return len(s.a), len(s.b) }
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func (s bytesSeqs) commonPrefixLen(ai, aj, bi, bj int) int {
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return commonPrefixLenBytes(s.a[ai:aj:aj], s.b[bi:bj:bj])
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}
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func (s bytesSeqs) commonSuffixLen(ai, aj, bi, bj int) int {
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return commonSuffixLenBytes(s.a[ai:aj:aj], s.b[bi:bj:bj])
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}
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type runesSeqs struct{ a, b []rune }
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func (s runesSeqs) lengths() (int, int) { return len(s.a), len(s.b) }
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func (s runesSeqs) commonPrefixLen(ai, aj, bi, bj int) int {
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return commonPrefixLenRunes(s.a[ai:aj:aj], s.b[bi:bj:bj])
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}
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func (s runesSeqs) commonSuffixLen(ai, aj, bi, bj int) int {
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return commonSuffixLenRunes(s.a[ai:aj:aj], s.b[bi:bj:bj])
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}
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// TODO(adonovan): optimize these functions using ideas from:
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// - https://go.dev/cl/408116 common.go
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// - https://go.dev/cl/421435 xor_generic.go
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// TODO(adonovan): factor using generics when available,
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// but measure performance impact.
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// commonPrefixLen* returns the length of the common prefix of a[ai:aj] and b[bi:bj].
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func commonPrefixLenBytes(a, b []byte) int {
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n := min(len(a), len(b))
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i := 0
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for i < n && a[i] == b[i] {
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i++
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}
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return i
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}
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func commonPrefixLenRunes(a, b []rune) int {
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n := min(len(a), len(b))
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i := 0
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for i < n && a[i] == b[i] {
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i++
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}
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return i
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}
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func commonPrefixLenString(a, b string) int {
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n := min(len(a), len(b))
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i := 0
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for i < n && a[i] == b[i] {
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i++
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}
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return i
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}
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// commonSuffixLen* returns the length of the common suffix of a[ai:aj] and b[bi:bj].
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func commonSuffixLenBytes(a, b []byte) int {
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n := min(len(a), len(b))
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i := 0
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for i < n && a[len(a)-1-i] == b[len(b)-1-i] {
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i++
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}
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return i
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}
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func commonSuffixLenRunes(a, b []rune) int {
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n := min(len(a), len(b))
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i := 0
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for i < n && a[len(a)-1-i] == b[len(b)-1-i] {
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i++
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}
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return i
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}
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func commonSuffixLenString(a, b string) int {
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n := min(len(a), len(b))
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i := 0
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for i < n && a[len(a)-1-i] == b[len(b)-1-i] {
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i++
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}
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return i
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}
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func min(x, y int) int {
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if x < y {
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return x
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} else {
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return y
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}
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}
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