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| 1 | +// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file |
| 2 | +// for details. All rights reserved. Use of this source code is governed by a |
| 3 | +// BSD-style license that can be found in the LICENSE file. |
| 4 | + |
| 5 | +// ignore_for_file: invalid_use_of_visible_for_testing_member |
| 6 | + |
| 7 | +import 'dart:math'; |
| 8 | + |
| 9 | +import 'license_detector.dart' show Token; |
| 10 | + |
| 11 | +/// A pair representing matching tokens from unknown to known sequences. |
| 12 | +typedef TokenPair = ({Token unknown, Token known}); |
| 13 | + |
| 14 | +/// Calculates the longest common subsequence (LCS) between [unknown] and [known] token lists. |
| 15 | +/// |
| 16 | +/// Tokens are compared using their normalized [Token.value]. Returns the longest |
| 17 | +/// common subsequence as a list of [TokenPair] objects containing references to |
| 18 | +/// both the unknown and known tokens that match. |
| 19 | +List<TokenPair> longestCommonSubsequence({ |
| 20 | + required List<Token> unknown, |
| 21 | + required List<Token> known, |
| 22 | +}) { |
| 23 | + final maxPrefixLength = min(unknown.length, known.length); |
| 24 | + if (maxPrefixLength == 0) { |
| 25 | + return []; |
| 26 | + } |
| 27 | + |
| 28 | + final matchedPrefix = <TokenPair>[]; |
| 29 | + for (var i = 0; i < maxPrefixLength; i++) { |
| 30 | + final utoken = unknown[i]; |
| 31 | + final ktoken = known[i]; |
| 32 | + if (utoken.value != ktoken.value) { |
| 33 | + break; |
| 34 | + } |
| 35 | + matchedPrefix.add((unknown: utoken, known: ktoken)); |
| 36 | + } |
| 37 | + |
| 38 | + final maxPostfixLength = maxPrefixLength - matchedPrefix.length; |
| 39 | + final matchedPostfix = <TokenPair>[]; |
| 40 | + var matchedPostfixCount = 0; |
| 41 | + for (var i = 1; i <= maxPostfixLength; i++) { |
| 42 | + final utoken = unknown[unknown.length - i]; |
| 43 | + final ktoken = known[known.length - i]; |
| 44 | + if (utoken.value != ktoken.value) { |
| 45 | + break; |
| 46 | + } |
| 47 | + matchedPostfixCount++; |
| 48 | + } |
| 49 | + for (var i = matchedPostfixCount; i >= 1; i--) { |
| 50 | + final utoken = unknown[unknown.length - i]; |
| 51 | + final ktoken = known[known.length - i]; |
| 52 | + matchedPostfix.add((unknown: utoken, known: ktoken)); |
| 53 | + } |
| 54 | + |
| 55 | + List<Token> trimList(List<Token> list) { |
| 56 | + if (matchedPrefix.isEmpty && matchedPostfix.isEmpty) { |
| 57 | + return list; |
| 58 | + } |
| 59 | + return list |
| 60 | + .skip(matchedPrefix.length) |
| 61 | + .take(list.length - matchedPrefix.length - matchedPostfix.length) |
| 62 | + .toList(); |
| 63 | + } |
| 64 | + |
| 65 | + return [ |
| 66 | + ...matchedPrefix, |
| 67 | + ..._dynamicLcs(unknown: trimList(unknown), known: trimList(known)), |
| 68 | + ...matchedPostfix, |
| 69 | + ]; |
| 70 | +} |
| 71 | + |
| 72 | +Iterable<TokenPair> _dynamicLcs({ |
| 73 | + required List<Token> unknown, |
| 74 | + required List<Token> known, |
| 75 | +}) { |
| 76 | + if (unknown.isEmpty || known.isEmpty) { |
| 77 | + return []; |
| 78 | + } |
| 79 | + final m = unknown.length; |
| 80 | + final n = known.length; |
| 81 | + |
| 82 | + // table to store lengths of LCS |
| 83 | + final table = List.generate(m + 1, (_) => List.filled(n + 1, 0)); |
| 84 | + for (var i = 1; i <= m; i++) { |
| 85 | + for (var j = 1; j <= n; j++) { |
| 86 | + if (unknown[i - 1].value == known[j - 1].value) { |
| 87 | + table[i][j] = table[i - 1][j - 1] + 1; |
| 88 | + } else { |
| 89 | + table[i][j] = max(table[i - 1][j], table[i][j - 1]); |
| 90 | + } |
| 91 | + } |
| 92 | + } |
| 93 | + |
| 94 | + // backtrack to construct the sequence |
| 95 | + final matchesBackwards = <TokenPair>[]; |
| 96 | + var i = m; |
| 97 | + var j = n; |
| 98 | + |
| 99 | + while (i > 0 && j > 0) { |
| 100 | + if (unknown[i - 1].value == known[j - 1].value) { |
| 101 | + // building backwards, will need to reverse the list |
| 102 | + matchesBackwards.add((unknown: unknown[i - 1], known: known[j - 1])); |
| 103 | + i--; |
| 104 | + j--; |
| 105 | + } else if (table[i - 1][j] > table[i][j - 1]) { |
| 106 | + i--; |
| 107 | + } else { |
| 108 | + j--; |
| 109 | + } |
| 110 | + } |
| 111 | + return matchesBackwards.reversed; |
| 112 | +} |
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