Add day 15 solution

day15.chpl

@@ -0,0 +1,96 @@
+use IO, Set, List;
+
+iter data() {
+  var x1, y1, x2, y2 = 0;
+  while readf("Sensor at x=%i, y=%i: closest beacon is at x=%i, y=%i\n", x1, y1, x2, y2) {
+    yield ((x1, y1), (x2, y2), abs(x1-x2) + abs(y1-y2));
+  }
+}
+
+iter positions((x1,y1), len) {
+  for l in 0..len {
+    for (dx, dy) in zip(0..l, 0..l by -1) {
+      yield (x1+dx, y1+dy);
+      yield (x1+dx, y1-dy);
+      yield (x1-dx, y1+dy);
+      yield (x1-dx, y1-dy);
+    }
+  }
+}
+
+record overlapping {
+  var disjoint: list(range(int));
+
+  proc add(arg: range(int)) {
+    // Don't pollute `disjoint`.
+    if arg.isEmpty() then return;
+
+    var newRng = arg;
+    do {
+      var merged = false;
+      for (rng, i) in zip(disjoint, 0..) {
+        if newRng[rng].isEmpty() then continue;
+        newRng = min(rng.lowBound, newRng.lowBound)..max(rng.highBound, newRng.highBound);
+        disjoint.pop(i);
+        merged = true;
+        break;
+      }
+    } while merged;
+    disjoint.append(newRng);
+  }
+
+  iter these() { for rng in disjoint do yield rng; }
+  proc size { return + [rng in this] rng.size; }
+  proc boundedSize(bound) { return + reduce [rng in this] rng[bound].size; }
+  proc contains(x) { return || reduce [rng in this] rng.contains(x); }
+}
+
+enum axis { xAxis = 0, yAxis = 1 };
+use axis;
+
+proc ((int, int)).rangeAlong(axs: axis, reach: int, theXOrY: int) {
+  const dim = axs : int;
+  const dist = abs(this[dim]-theXOrY);
+
+  // Too far
+  if dist > reach then return 0..<0;
+
+  // Get the range
+  const remDist = max(0, reach-dist);
+  return (this[1-dim]-remDist)..(this[1-dim]+remDist);
+}
+
+
+config const theY = 10;
+const searchSpace = 0..theY * 2;
+const input = data();
+
+// Solve part 1
+var overlaps: overlapping;
+var occupied: set((int, int));
+for (sensor, beacon, reach) in input {
+  occupied.add(sensor);
+  occupied.add(beacon);
+  overlaps.add(sensor.rangeAlong(yAxis, reach, theY));
+}
+writeln(overlaps.size - (+ reduce [(x,y) in occupied] if y == theY then 1));
+
+// Solve part 2
+forall checkY in searchSpace {
+  var overlaps: overlapping;
+  for (sensor, _, reach) in input {
+    overlaps.add(sensor.rangeAlong(yAxis, reach, checkY));
+  }
+
+  if overlaps.boundedSize(searchSpace) != searchSpace.size {
+    // Found the y-cordinate. Now find the x-coordinate.
+    for checkX in searchSpace {
+      if !overlaps.contains(checkX) {
+        // x-coord isn't in the interval, so we found our answer.
+        writeln("x = ", checkX, ", y = ", checkY, ", frequency = ", checkX * 4000000 + checkY);
+        break;
+      }
+    }
+  }
+}
+