dartterm/lib/algorithms/regionalize.dart

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