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65 lines
2.2 KiB
65 lines
2.2 KiB
6 years ago
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// Copyright (c) 2018 Couchbase, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package levenshtein2
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import "fmt"
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// StateLimit is the maximum number of states allowed
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const StateLimit = 10000
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// ErrTooManyStates is returned if you attempt to build a Levenshtein
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// automaton which requires too many states.
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var ErrTooManyStates = fmt.Errorf("dfa contains more than %d states",
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StateLimit)
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// LevenshteinAutomatonBuilder wraps a precomputed
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// datastructure that allows to produce small (but not minimal) DFA.
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type LevenshteinAutomatonBuilder struct {
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pDfa *ParametricDFA
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}
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// NewLevenshteinAutomatonBuilder creates a
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// reusable, threadsafe Levenshtein automaton builder.
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// `maxDistance` - maximum distance considered by the automaton.
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// `transposition` - assign a distance of 1 for transposition
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//
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// Building this automaton builder is computationally intensive.
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// While it takes only a few milliseconds for `d=2`, it grows
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// exponentially with `d`. It is only reasonable to `d <= 5`.
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func NewLevenshteinAutomatonBuilder(maxDistance uint8,
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transposition bool) (*LevenshteinAutomatonBuilder, error) {
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lnfa := newLevenshtein(maxDistance, transposition)
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pdfa, err := fromNfa(lnfa)
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if err != nil {
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return nil, err
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}
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return &LevenshteinAutomatonBuilder{pDfa: pdfa}, nil
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}
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// BuildDfa builds the levenshtein automaton for serving
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// queries with a given edit distance.
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func (lab *LevenshteinAutomatonBuilder) BuildDfa(query string,
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fuzziness uint8) (*DFA, error) {
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return lab.pDfa.buildDfa(query, fuzziness, false)
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}
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// MaxDistance returns the MaxEdit distance supported by the
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// LevenshteinAutomatonBuilder builder.
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func (lab *LevenshteinAutomatonBuilder) MaxDistance() uint8 {
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return lab.pDfa.maxDistance
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}
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