67 lines
1.8 KiB
Dart
67 lines
1.8 KiB
Dart
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import 'dart:math' as math;
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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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Region(this.rect, this.points);
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static 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, yMax));
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Region(rect, s);
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}
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}
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List<Region> regionalize(
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math.Rectangle<int> 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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void floodfill(int x, int y, region) {
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if (!rect.containsPoint(math.Point(x, y))) {
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return;
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}
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if (regions[(x, y)] != null) {
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return;
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}
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if (!isAccessible(x, y)) {
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return;
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}
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regions[(x, y)] = region;
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floodfill(x - 1, y, region);
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floodfill(x + 1, y, region);
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floodfill(x, y - 1, region);
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floodfill(x, y + 1, region);
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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.top; y < rect.bottom; y++) {
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for (var x = rect.left; x < rect.right; x++) {
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if (regions[(x, y)] == null) {
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floodfill(x, y, nextRegion);
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nextRegion += 1;
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}
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}
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}
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return _toExplicit(regions);
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}
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List<Region> _toExplicit(Map<(int, int), int> regions) {
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List<Set<(int, int)>> pointsOut = [
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for (var i = 0; i < regions.length; i++) Set()
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];
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for (var MapEntry(key: (x, y), value: id_) in regions.entries) {
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pointsOut[id_].add((x, y));
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}
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return [for (var s in pointsOut) Region.fromNonEmptySet(s)];
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}
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