LLVM 20.0.0git
edit_distance.h
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1//===-- llvm/ADT/edit_distance.h - Array edit distance function --- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8///
9/// \file
10/// This file defines a Levenshtein distance function that works for any two
11/// sequences, with each element of each sequence being analogous to a character
12/// in a string.
13///
14//===----------------------------------------------------------------------===//
15
16#ifndef LLVM_ADT_EDIT_DISTANCE_H
17#define LLVM_ADT_EDIT_DISTANCE_H
18
19#include "llvm/ADT/ArrayRef.h"
20#include <algorithm>
21
22namespace llvm {
23
24/// Determine the edit distance between two sequences.
25///
26/// \param FromArray the first sequence to compare.
27///
28/// \param ToArray the second sequence to compare.
29///
30/// \param Map A Functor to apply to each item of the sequences before
31/// comparison.
32///
33/// \param AllowReplacements whether to allow element replacements (change one
34/// element into another) as a single operation, rather than as two operations
35/// (an insertion and a removal).
36///
37/// \param MaxEditDistance If non-zero, the maximum edit distance that this
38/// routine is allowed to compute. If the edit distance will exceed that
39/// maximum, returns \c MaxEditDistance+1.
40///
41/// \returns the minimum number of element insertions, removals, or (if
42/// \p AllowReplacements is \c true) replacements needed to transform one of
43/// the given sequences into the other. If zero, the sequences are identical.
44template <typename T, typename Functor>
46 Functor Map, bool AllowReplacements = true,
47 unsigned MaxEditDistance = 0) {
48 // The algorithm implemented below is the "classic"
49 // dynamic-programming algorithm for computing the Levenshtein
50 // distance, which is described here:
51 //
52 // http://en.wikipedia.org/wiki/Levenshtein_distance
53 //
54 // Although the algorithm is typically described using an m x n
55 // array, only one row plus one element are used at a time, so this
56 // implementation just keeps one vector for the row. To update one entry,
57 // only the entries to the left, top, and top-left are needed. The left
58 // entry is in Row[x-1], the top entry is what's in Row[x] from the last
59 // iteration, and the top-left entry is stored in Previous.
60 typename ArrayRef<T>::size_type m = FromArray.size();
61 typename ArrayRef<T>::size_type n = ToArray.size();
62
63 if (MaxEditDistance) {
64 // If the difference in size between the 2 arrays is larger than the max
65 // distance allowed, we can bail out as we will always need at least
66 // MaxEditDistance insertions or removals.
67 typename ArrayRef<T>::size_type AbsDiff = m > n ? m - n : n - m;
68 if (AbsDiff > MaxEditDistance)
69 return MaxEditDistance + 1;
70 }
71
73 for (unsigned i = 1; i < Row.size(); ++i)
74 Row[i] = i;
75
76 for (typename ArrayRef<T>::size_type y = 1; y <= m; ++y) {
77 Row[0] = y;
78 unsigned BestThisRow = Row[0];
79
80 unsigned Previous = y - 1;
81 const auto &CurItem = Map(FromArray[y - 1]);
82 for (typename ArrayRef<T>::size_type x = 1; x <= n; ++x) {
83 int OldRow = Row[x];
84 if (AllowReplacements) {
85 Row[x] = std::min(Previous + (CurItem == Map(ToArray[x - 1]) ? 0u : 1u),
86 std::min(Row[x - 1], Row[x]) + 1);
87 }
88 else {
89 if (CurItem == Map(ToArray[x - 1]))
90 Row[x] = Previous;
91 else Row[x] = std::min(Row[x-1], Row[x]) + 1;
92 }
93 Previous = OldRow;
94 BestThisRow = std::min(BestThisRow, Row[x]);
95 }
96
97 if (MaxEditDistance && BestThisRow > MaxEditDistance)
98 return MaxEditDistance + 1;
99 }
100
101 unsigned Result = Row[n];
102 return Result;
103}
104
105template <typename T>
106unsigned ComputeEditDistance(ArrayRef<T> FromArray, ArrayRef<T> ToArray,
107 bool AllowReplacements = true,
108 unsigned MaxEditDistance = 0) {
110 FromArray, ToArray, [](const T &X) -> const T & { return X; },
111 AllowReplacements, MaxEditDistance);
112}
113
114} // End llvm namespace
115
116#endif
static GCMetadataPrinterRegistry::Add< ErlangGCPrinter > X("erlang", "erlang-compatible garbage collector")
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory),...
Definition: ArrayRef.h:41
size_t size_type
Definition: ArrayRef.h:52
size_t size() const
size - Get the array size.
Definition: ArrayRef.h:165
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1209
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
unsigned ComputeEditDistance(ArrayRef< T > FromArray, ArrayRef< T > ToArray, bool AllowReplacements=true, unsigned MaxEditDistance=0)
unsigned ComputeMappedEditDistance(ArrayRef< T > FromArray, ArrayRef< T > ToArray, Functor Map, bool AllowReplacements=true, unsigned MaxEditDistance=0)
Determine the edit distance between two sequences.
Definition: edit_distance.h:45