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86 lines
2 KiB
Go
86 lines
2 KiB
Go
// Copyright 2016 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 stringset provides a way to represent a collection of strings
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// compactly.
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package stringset
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import "sort"
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// A Set holds a collection of strings that can be looked up by an index number.
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type Set struct {
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// These fields are exported to allow for code generation.
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Data string
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Index []uint16
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}
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// Elem returns the string with index i. It panics if i is out of range.
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func (s *Set) Elem(i int) string {
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return s.Data[s.Index[i]:s.Index[i+1]]
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}
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// Len returns the number of strings in the set.
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func (s *Set) Len() int {
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return len(s.Index) - 1
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}
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// Search returns the index of the given string or -1 if it is not in the set.
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// The Set must have been created with strings in sorted order.
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func Search(s *Set, str string) int {
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// TODO: optimize this if it gets used a lot.
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n := len(s.Index) - 1
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p := sort.Search(n, func(i int) bool {
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return s.Elem(i) >= str
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})
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if p == n || str != s.Elem(p) {
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return -1
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}
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return p
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}
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// A Builder constructs Sets.
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type Builder struct {
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set Set
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index map[string]int
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}
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// NewBuilder returns a new and initialized Builder.
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func NewBuilder() *Builder {
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return &Builder{
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set: Set{
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Index: []uint16{0},
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},
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index: map[string]int{},
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}
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}
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// Set creates the set created so far.
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func (b *Builder) Set() Set {
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return b.set
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}
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// Index returns the index for the given string, which must have been added
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// before.
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func (b *Builder) Index(s string) int {
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return b.index[s]
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}
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// Add adds a string to the index. Strings that are added by a single Add will
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// be stored together, unless they match an existing string.
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func (b *Builder) Add(ss ...string) {
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// First check if the string already exists.
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for _, s := range ss {
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if _, ok := b.index[s]; ok {
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continue
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}
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b.index[s] = len(b.set.Index) - 1
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b.set.Data += s
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x := len(b.set.Data)
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if x > 0xFFFF {
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panic("Index too > 0xFFFF")
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}
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b.set.Index = append(b.set.Index, uint16(x))
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}
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}
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