103 lines
3.6 KiB
C++
103 lines
3.6 KiB
C++
//===-- 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
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// 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
|