77 lines
2.1 KiB
Dart
77 lines
2.1 KiB
Dart
import 'dart:math' as math;
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import 'package:dartterm/algorithms/geometry.dart' as geo;
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class Region {
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final math.Rectangle<int> rect;
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final Set<(int, int)> points;
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bool get isRectangle => points.length == rect.width * rect.height;
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Region(this.rect, this.points);
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static Region fromNonEmptySet(Set<(int, int)> s) {
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assert(s.isNotEmpty);
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int xMin = s.map<int>((xy) => xy.$1).reduce(math.min);
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int yMin = s.map<int>((xy) => xy.$2).reduce(math.min);
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int xMax = s.map<int>((xy) => xy.$1).reduce(math.max);
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int yMax = s.map<int>((xy) => xy.$2).reduce(math.max);
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var rect = math.Rectangle.fromPoints(
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math.Point(xMin, yMin), math.Point(xMax + 1, yMax + 1));
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return Region(rect, s);
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}
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@override
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String toString() {
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return "Region($rect, $points)";
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}
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}
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List<Region> regionalize(geo.Rect rect, bool Function(int, int) isAccessible) {
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int nextRegion = 0;
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Map<(int, int), int> regions = {};
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int floodfill(int x, int y) {
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int workDone = 0;
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if (!rect.containsPoint(geo.Offset(x, y))) {
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return workDone;
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}
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if (regions[(x, y)] != null) {
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return workDone;
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}
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if (!isAccessible(x, y)) {
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return workDone;
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}
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regions[(x, y)] = nextRegion;
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workDone += 1;
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workDone += floodfill(x - 1, y);
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workDone += floodfill(x + 1, y);
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workDone += floodfill(x, y - 1);
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workDone += floodfill(x, y + 1);
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return workDone;
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}
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// TODO: This can be done more efficiently with a union/find data structure
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// But this is an easy implementation to understand
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for (var y = rect.y0; y < rect.y1; y++) {
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for (var x = rect.x0; x < rect.x1; x++) {
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if (regions[(x, y)] == null) {
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if (floodfill(x, y) > 0) {
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nextRegion += 1;
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}
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}
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}
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}
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return _toExplicit(regions, nextRegion);
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}
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List<Region> _toExplicit(Map<(int, int), int> pointRegions, int nRegions) {
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List<Set<(int, int)>> regionPoints = [for (var i = 0; i < nRegions; i++) {}];
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for (var MapEntry(key: (x, y), value: id_) in pointRegions.entries) {
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regionPoints[id_].add((x, y));
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}
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return [for (var s in regionPoints) Region.fromNonEmptySet(s)];
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}
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