83 lines
1.9 KiB
Dart
83 lines
1.9 KiB
Dart
class Heap<T> {
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final int Function(T) getPriority;
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List<(T, int)> _items;
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Heap({
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required this.getPriority
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}): _items = [];
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factory Heap.fromItems(
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List<T> items,
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{
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required int Function(T) getPriority,
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}
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) {
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Heap<T> heap = Heap(getPriority: getPriority);
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for (final T item in items) {
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heap.add(item);
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}
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return heap;
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}
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T get first => _items.first.$1;
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T? get firstOrNull => _items.firstOrNull?.$1;
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int get length => _items.length;
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bool get isEmpty => _items.isEmpty;
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bool get isNotEmpty => _items.isNotEmpty;
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void add(T item) {
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final (T, int) heapItem = (item, getPriority(item));
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final int thisKey = heapItem.$2;
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int i = _items.length;
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_items.add(heapItem);
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while (i > 0 && _items[(i-1) ~/ 2].$2 > thisKey) {
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_items[i] = _items[(i-1) ~/ 2];
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i = (i-1)~/2;
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}
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_items[i] = heapItem;
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}
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T removeFirst() {
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if (_items.isEmpty) {
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throw StateError("No element");
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}
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final T firstItem = _items[0].$1;
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if (_items.length < 2) {
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_items.length--;
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return firstItem;
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}
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final (T, int) itemToMove = _items.last;
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_items[0] = itemToMove;
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_items.length--;
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int i = 0;
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int leftIndex, rightIndex;
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bool stop = false;
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while (!stop) {
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rightIndex = (i+1) << 1;
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leftIndex = rightIndex-1;
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if (leftIndex < _items.length && itemToMove.$2 > _items[leftIndex].$2) {
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if (rightIndex < _items.length && _items[leftIndex].$2 > _items[rightIndex].$2) {
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_items[i] = _items[rightIndex];
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_items[rightIndex] = itemToMove;
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i = rightIndex;
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} else {
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_items[i] = _items[leftIndex];
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_items[leftIndex] = itemToMove;
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i = leftIndex;
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}
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} else {
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stop = true;
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}
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}
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return firstItem;
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}
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@override
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String toString() => _items.map(((T, int) item) => item.$1).toString();
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} |