| | 1 | | using MoreLinq; |
| | 2 | | using MoreStructures.Utilities; |
| | 3 | |
|
| | 4 | | namespace MoreStructures.Lists.Searching; |
| | 5 | |
|
| | 6 | | /// <inheritdoc path="//*[not(self::summary or self::remarks)]"/> |
| | 7 | | /// |
| | 8 | | /// <summary> |
| | 9 | | /// An object able to search in linear time for items in direct random access structures, such as lists and |
| | 10 | | /// arrays, which are monodimensional and implement the <see cref="IEnumerable{T}"/> interface. |
| | 11 | | /// </summary> |
| | 12 | | /// <remarks> |
| | 13 | | /// <inheritdoc cref="ISearch"/> |
| | 14 | | /// <br/> |
| | 15 | | /// Unlike <see cref="BinarySearch"/>, this implementation doesn't make any assumption on the order of items in |
| | 16 | | /// in the data structure. |
| | 17 | | /// </remarks> |
| | 18 | | public class LinearSearch : ISearch |
| | 19 | | { |
| | 20 | | private static IEnumerable<KeyValuePair<int, T>> GetIndexedItemsInRangeEqualTo<T>( |
| | 21 | | IEnumerable<T> source, T item, IComparer<T>? comparer, int? fromIndex, int? toIndex, bool reverse) |
| 540 | 22 | | { |
| 540 | 23 | | var length = SearchHelperMethods.ValidateIndexesAndGetLength(source, fromIndex, toIndex); |
| 531 | 24 | | fromIndex ??= 0; |
| 531 | 25 | | toIndex ??= length - 1; |
| | 26 | |
|
| 531 | 27 | | comparer ??= Comparer<T>.Default; |
| | 28 | |
|
| 531 | 29 | | var count = toIndex.Value! - fromIndex.Value! + 1; |
| | 30 | |
|
| 531 | 31 | | var indexes = Enumerable.Range(fromIndex.Value!, count); |
| | 32 | |
|
| 531 | 33 | | if (reverse) |
| 62 | 34 | | { |
| 62 | 35 | | source = source.Reverse(); |
| 635 | 36 | | indexes = indexes.Select(i => count - 1 - i); |
| 62 | 37 | | } |
| | 38 | |
|
| 531 | 39 | | return source |
| 531 | 40 | | .SkipO1(fromIndex.Value!) |
| 531 | 41 | | .Take(count) |
| 531 | 42 | | .Zip(indexes) |
| 3489 | 43 | | .Where(c => comparer.Compare(c.First, item) == 0) |
| 1161 | 44 | | .Select(c => KeyValuePair.Create(c.Second, c.First)); |
| 531 | 45 | | } |
| | 46 | |
|
| | 47 | | /// <inheritdoc path="//*[not(self::summary or self::remarks)]"/> |
| | 48 | | /// <summary> |
| | 49 | | /// <inheritdoc/> |
| | 50 | | /// <br/> |
| | 51 | | /// This specific implementation does not make any assunption on <paramref name="source"/> being sorted. |
| | 52 | | /// </summary> |
| | 53 | | /// <remarks> |
| | 54 | | /// The algorithm linearly scans the search space from <paramref name="fromIndex"/> to <paramref name="toIndex"/>, |
| | 55 | | /// one index at every iteration, reducing it linearly to a single item or to an empty set. |
| | 56 | | /// <br/> |
| | 57 | | /// Time Complexity = O(n), Space Complexity = O(1), where n = number of items between |
| | 58 | | /// <paramref name="fromIndex"/> and <paramref name="toIndex"/>. |
| | 59 | | /// </remarks> |
| | 60 | | public int First<T>( |
| | 61 | | IEnumerable<T> source, T item, IComparer<T>? comparer = null, int? fromIndex = null, int? toIndex = null) => |
| | 62 | |
|
| 347 | 63 | | GetIndexedItemsInRangeEqualTo(source, item, comparer, fromIndex, toIndex, false) |
| 336 | 64 | | .Select(e => e.Key as int?) |
| 347 | 65 | | .FirstOrDefault(-1)! |
| 347 | 66 | | .Value; |
| | 67 | |
|
| | 68 | | /// <inheritdoc path="//*[not(self::summary or self::remarks)]"/> |
| | 69 | | /// <summary> |
| | 70 | | /// <inheritdoc/> |
| | 71 | | /// <br/> |
| | 72 | | /// This specific implementation does not make any assunption on <paramref name="source"/> being sorted. |
| | 73 | | /// </summary> |
| | 74 | | /// <remarks> |
| | 75 | | /// <para id="algo"> |
| | 76 | | /// ALGORITHM |
| | 77 | | /// <br/> |
| | 78 | | /// The algorithm linearly scans the search space from <paramref name="fromIndex"/> to |
| | 79 | | /// <paramref name="toIndex"/>, one index at every iteration, collecting first occurrences into a |
| | 80 | | /// <see cref="IDictionary{TKey, TValue}"/>. |
| | 81 | | /// </para> |
| | 82 | | /// <para id="complexity"> |
| | 83 | | /// COMPLEXITY |
| | 84 | | /// <br/> |
| | 85 | | /// Time Complexity = O(n), Space Complexity = O(sigma), where: |
| | 86 | | /// <br/> |
| | 87 | | /// - n is the <b>number of items</b> between <paramref name="fromIndex"/> and <paramref name="toIndex"/>. |
| | 88 | | /// <br/> |
| | 89 | | /// - For "large alphabets" scenarios (such as when the alphabet is int - 2^32 possible values, but |
| | 90 | | /// <paramref name="source"/> is way smaller than that), sigma is the <b>number of distinct elements </b> of |
| | 91 | | /// <paramref name="source"/>. |
| | 92 | | /// <br/> |
| | 93 | | /// - For "small alphabets" scenarios (such as when the alphabet is comprised of few symbols only), sigma is |
| | 94 | | /// the size of the alphabet. |
| | 95 | | /// <br/> |
| | 96 | | /// - In either scenario the worst case of the O(sigma) Space Complexity is O(n), which is when all the symbols |
| | 97 | | /// in <paramref name="source"/> are different from each other). |
| | 98 | | /// </para> |
| | 99 | | /// </remarks> |
| | 100 | | public IDictionary<T, int> FirstAll<T>( |
| | 101 | | IEnumerable<T> source, IComparer<T>? comparer = null, int? fromIndex = null, int? toIndex = null) |
| | 102 | | where T : notnull |
| 88 | 103 | | { |
| 88 | 104 | | var length = SearchHelperMethods.ValidateIndexesAndGetLength(source, fromIndex, toIndex); |
| 84 | 105 | | fromIndex ??= 0; |
| 84 | 106 | | toIndex ??= length - 1; |
| | 107 | |
|
| 84 | 108 | | var result = new Dictionary<T, int> { }; |
| | 109 | |
|
| 84 | 110 | | var sourceWindow = source |
| 84 | 111 | | .SkipO1(fromIndex.Value!) |
| 84 | 112 | | .Take(toIndex.Value! - fromIndex.Value! + 1); |
| | 113 | |
|
| 84 | 114 | | var index = fromIndex.Value!; |
| 3024 | 115 | | foreach (var item in sourceWindow) |
| 1386 | 116 | | { |
| 1386 | 117 | | if (!result.TryGetValue(item, out var value)) |
| 741 | 118 | | result[item] = index; |
| 1386 | 119 | | index++; |
| 1386 | 120 | | } |
| | 121 | |
|
| 84 | 122 | | return result; |
| 84 | 123 | | } |
| | 124 | |
|
| | 125 | | /// <inheritdoc path="//*[not(self::summary or self::remarks)]"/> |
| | 126 | | /// <summary> |
| | 127 | | /// <inheritdoc/> |
| | 128 | | /// <br/> |
| | 129 | | /// This specific implementation does not make any assunption on <paramref name="source"/> being sorted. |
| | 130 | | /// </summary> |
| | 131 | | /// <remarks> |
| | 132 | | /// The algorithm linearly scans the search space from <paramref name="toIndex"/> to <paramref name="fromIndex"/>, |
| | 133 | | /// one index at every iteration, reducing it linearly to a single item or to an empty set. |
| | 134 | | /// <br/> |
| | 135 | | /// Time Complexity = O(n), Space Complexity = O(1), where n = number of items between <paramref name="fromIndex"/> |
| | 136 | | /// and <paramref name="toIndex"/>. |
| | 137 | | /// </remarks> |
| | 138 | | public int Last<T>( |
| | 139 | | IEnumerable<T> source, T item, IComparer<T>? comparer = null, int? fromIndex = null, int? toIndex = null) => |
| | 140 | |
|
| 66 | 141 | | GetIndexedItemsInRangeEqualTo(source, item, comparer, fromIndex, toIndex, true) |
| 58 | 142 | | .Select(e => e.Key as int?) |
| 66 | 143 | | .FirstOrDefault(-1)! |
| 66 | 144 | | .Value; |
| | 145 | |
|
| | 146 | | /// <inheritdoc path="//*[not(self::summary or self::remarks)]"/> |
| | 147 | | /// <summary> |
| | 148 | | /// <inheritdoc/> |
| | 149 | | /// <br/> |
| | 150 | | /// This specific implementation does not make any assunption on <paramref name="source"/> being sorted. |
| | 151 | | /// </summary> |
| | 152 | | /// <remarks> |
| | 153 | | /// The algorithm linearly scans the search space from <paramref name="fromIndex"/> to <paramref name="toIndex"/>, |
| | 154 | | /// one index at every iteration. |
| | 155 | | /// <br/> |
| | 156 | | /// It just stores the smallest and the biggest index among the ones which correspond to items equal to |
| | 157 | | /// <paramref name="item"/>. So it has constant, and not linear, space requirements. |
| | 158 | | /// <br/> |
| | 159 | | /// Time Complexity = O(n), Space Complexity = O(1), where n = number of items between <paramref name="fromIndex"/> |
| | 160 | | /// and <paramref name="toIndex"/>. |
| | 161 | | /// </remarks> |
| | 162 | | public (int first, int last) Interval<T>( |
| | 163 | | IEnumerable<T> source, T item, IComparer<T>? comparer = null, int? fromIndex = null, int? toIndex = null) => |
| | 164 | |
|
| 62 | 165 | | GetIndexedItemsInRangeEqualTo(source, item, comparer, fromIndex, toIndex, false) |
| 136 | 166 | | .Select(e => e.Key) |
| 198 | 167 | | .Aggregate((-1, -1), (acc, i) => ( |
| 198 | 168 | | acc.Item1 < 0 ? i : Math.Min(acc.Item1, i), |
| 198 | 169 | | acc.Item2 < 0 ? i : Math.Max(acc.Item2, i))); |
| | 170 | |
|
| | 171 | | /// <inheritdoc path="//*[not(self::summary or self::remarks)]"/> |
| | 172 | | /// <summary> |
| | 173 | | /// <inheritdoc/> |
| | 174 | | /// <br/> |
| | 175 | | /// This specific implementation does not make any assunption on <paramref name="source"/> being sorted. |
| | 176 | | /// </summary> |
| | 177 | | /// <remarks> |
| | 178 | | /// The algorithm linearly scans the search space from <paramref name="toIndex"/> to <paramref name="fromIndex"/>, |
| | 179 | | /// one index at every iteration, reducing it linearly to a single item or to an empty set. |
| | 180 | | /// <br/> |
| | 181 | | /// It just stores the current counter of occurrences of <paramref name="item"/> in <paramref name="source"/>, |
| | 182 | | /// not all of them. So it has constant, and not linear, space requirements. |
| | 183 | | /// <br/> |
| | 184 | | /// Time Complexity = O(n), Space Complexity = O(1), where n = number of items between |
| | 185 | | /// <paramref name="fromIndex"/> and <paramref name="toIndex"/>. |
| | 186 | | /// </remarks> |
| | 187 | | public int Nth<T>( |
| | 188 | | IEnumerable<T> source, T item, int occurrenceRank, IComparer<T>? comparer = null, int? fromIndex = null, |
| | 189 | | int? toIndex = null) |
| 66 | 190 | | { |
| 66 | 191 | | if (occurrenceRank < 0) |
| 1 | 192 | | throw new ArgumentOutOfRangeException(nameof(occurrenceRank), "Must be non-negative."); |
| | 193 | |
|
| 65 | 194 | | return GetIndexedItemsInRangeEqualTo(source, item, comparer, fromIndex, toIndex, false) |
| 100 | 195 | | .Select(e => e.Key as int?) |
| 65 | 196 | | .ElementAtOrDefault(occurrenceRank) ?? -1; |
| 65 | 197 | | } |
| | 198 | | } |