1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
|
#pragma once
#ifdef __GNUC__
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"
#endif
//===-- llvm/ADT/edit_distance.h - Array edit distance function --- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file defines a Levenshtein distance function that works for any two
/// sequences, with each element of each sequence being analogous to a character
/// in a string.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_EDIT_DISTANCE_H
#define LLVM_ADT_EDIT_DISTANCE_H
#include "llvm/ADT/ArrayRef.h"
#include <algorithm>
#include <memory>
namespace llvm {
/// Determine the edit distance between two sequences.
///
/// \param FromArray the first sequence to compare.
///
/// \param ToArray the second sequence to compare.
///
/// \param AllowReplacements whether to allow element replacements (change one
/// element into another) as a single operation, rather than as two operations
/// (an insertion and a removal).
///
/// \param MaxEditDistance If non-zero, the maximum edit distance that this
/// routine is allowed to compute. If the edit distance will exceed that
/// maximum, returns \c MaxEditDistance+1.
///
/// \returns the minimum number of element insertions, removals, or (if
/// \p AllowReplacements is \c true) replacements needed to transform one of
/// the given sequences into the other. If zero, the sequences are identical.
template<typename T>
unsigned ComputeEditDistance(ArrayRef<T> FromArray, ArrayRef<T> ToArray,
bool AllowReplacements = true,
unsigned MaxEditDistance = 0) {
// The algorithm implemented below is the "classic"
// dynamic-programming algorithm for computing the Levenshtein
// distance, which is described here:
//
// http://en.wikipedia.org/wiki/Levenshtein_distance
//
// Although the algorithm is typically described using an m x n
// array, only one row plus one element are used at a time, so this
// implementation just keeps one vector for the row. To update one entry,
// only the entries to the left, top, and top-left are needed. The left
// entry is in Row[x-1], the top entry is what's in Row[x] from the last
// iteration, and the top-left entry is stored in Previous.
typename ArrayRef<T>::size_type m = FromArray.size();
typename ArrayRef<T>::size_type n = ToArray.size();
const unsigned SmallBufferSize = 64;
unsigned SmallBuffer[SmallBufferSize];
std::unique_ptr<unsigned[]> Allocated;
unsigned *Row = SmallBuffer;
if (n + 1 > SmallBufferSize) {
Row = new unsigned[n + 1];
Allocated.reset(Row);
}
for (unsigned i = 1; i <= n; ++i)
Row[i] = i;
for (typename ArrayRef<T>::size_type y = 1; y <= m; ++y) {
Row[0] = y;
unsigned BestThisRow = Row[0];
unsigned Previous = y - 1;
for (typename ArrayRef<T>::size_type x = 1; x <= n; ++x) {
int OldRow = Row[x];
if (AllowReplacements) {
Row[x] = std::min(
Previous + (FromArray[y-1] == ToArray[x-1] ? 0u : 1u),
std::min(Row[x-1], Row[x])+1);
}
else {
if (FromArray[y-1] == ToArray[x-1]) Row[x] = Previous;
else Row[x] = std::min(Row[x-1], Row[x]) + 1;
}
Previous = OldRow;
BestThisRow = std::min(BestThisRow, Row[x]);
}
if (MaxEditDistance && BestThisRow > MaxEditDistance)
return MaxEditDistance + 1;
}
unsigned Result = Row[n];
return Result;
}
} // End llvm namespace
#endif
#ifdef __GNUC__
#pragma GCC diagnostic pop
#endif
|
