Add solution for 2021 day 17

2021/README.md

@@ -20,7 +20,7 @@
 | 14  |   ✓    |   ✓    | [Erlang]  |
 | 15  |   ✓    |   ✓    | [D]       |
 | 16  |   ✓    |   ✓    | [Haskell] |
-| 17  |        |        |           |
+| 17  |   ✓    |   ✓    | [Dart]    |
 | 18  |        |        |           |
 | 19  |        |        |           |
 | 20  |        |        |           |
@@ -52,3 +52,5 @@
 [erlang]: https://www.erlang.org
 [d]: https://dlang.org
 [haskell]: https://www.haskell.org
+[dart]: https://dart.dev
+[elixir]: https://elixir-lang.org

2021/day-17/Justfile

@@ -0,0 +1,2 @@
+@part PART INPUT_FILE="inputs/puzzle.txt":
+    dart part_{{PART}}.dart {{INPUT_FILE}}

2021/day-17/common.dart

@@ -0,0 +1,79 @@
+import "dart:io";
+import "dart:math";
+
+List<List<int>> parseFile(String path) {
+    final file = File(path);
+
+    final content = file.readAsStringSync();
+
+    final coordinates = content
+        .trim().split(" ")
+        .skip(2).where((e) => e.isNotEmpty)
+        .map((elem) {
+            return elem
+                .split("=").last
+                .replaceFirst(",", "").split("..")
+                .map(int.parse)
+                .toList();
+        })
+        .toList();
+
+  return coordinates;
+}
+
+List<int> step(int x, int y, int xv, int yv) {
+    final dx = x + xv;
+    final dy = y + yv;
+    final dxv = xv + (xv > 0 ? -1 : (xv < 0 ? 1 : 0));
+    final dyv = yv - 1;
+    return [dx, dy, dxv, dyv];
+}
+
+bool hasMissed(int x, int y, List<List<int>> area) {
+    var missed = (x - area[0][1]) > 0;
+    return missed || (y - area[1][0]) < 0;
+}
+
+bool isInTargetArea(int x, int y, List<List<int>> area) {
+    return
+        x >= area[0][0] &&
+        x <= area[0][1] &&
+        y >= area[1][0] &&
+        y <= area[1][1];
+}
+
+bool landsInTargetArea(int init_vx, int init_vy, List<List<int>> area) {
+    var x = 0;
+    var y = 0;
+    var vx = init_vx;
+    var vy = init_vy;
+
+    while (true) {
+        final result = step(x, y, vx, vy);
+        if (isInTargetArea(result[0], result[1], area)) return true;
+        if (hasMissed(result[0], result[1], area)) return false;
+        x = result[0];
+        y = result[1];
+        vx = result[2];
+        vy = result[3];
+    }
+}
+
+int? findMaxHeight(int init_vx, int init_vy, List<List<int>> area) {
+    var x = 0;
+    var y = 0;
+    var vx = init_vx;
+    var vy = init_vy;
+    var max_height = 0;
+
+    while (true) {
+        final result = step(x, y, vx, vy);
+        max_height = max(result[1], max_height);
+        if (isInTargetArea(result[0], result[1], area)) return max_height;
+        if (hasMissed(result[0], result[1], area)) return null;
+        x = result[0];
+        y = result[1];
+        vx = result[2];
+        vy = result[3];
+    }
+}

2021/day-17/inputs/puzzle.txt

@@ -0,0 +1 @@
+target area: x=277..318, y=-92..-53

2021/day-17/inputs/sample1.txt

@@ -0,0 +1 @@
+target area: x=20..30, y=-10..-5

2021/day-17/part_one.dart

@@ -0,0 +1,23 @@
+import "dart:math";
+import "common.dart";
+
+main(List<String> args) {
+    final path = args.first;
+
+    final target_area = parseFile(path);
+
+    final max_xv = target_area[0][1];
+    final max_yv = target_area[1][0].abs();
+    var max_height = 0;
+
+    Iterable.generate(max_xv, (v) => v + 1).forEach((x) {
+        Iterable.generate(max_yv, (v) => v + 1).forEach((y) {
+            final result = findMaxHeight(x, y, target_area);
+            if (result != null) {
+                max_height = max(result, max_height);
+            }
+        });
+    });
+
+    print(max_height);
+}

2021/day-17/part_two.dart

@@ -0,0 +1,30 @@
+import "dart:math";
+import "common.dart";
+
+main(List<String> args) {
+    final path = args.first;
+
+    final target_area = parseFile(path);
+
+    final max_xv = target_area[0][1];
+    final max_yv = target_area[1][0];
+    var velocity_count = 0;
+
+    var yv = max_yv;
+
+    while (yv < max_yv.abs()) {
+        var xv = max_xv;
+
+        while (xv > 0) {
+            if (landsInTargetArea(xv, yv, target_area)) {
+                velocity_count += 1;
+            }
+
+            xv -= 1;
+        }
+
+        yv += 1;
+    }
+
+    print(velocity_count);
+}

README.md

@@ -8,4 +8,4 @@
 -   [2018](2018/README.md) (0% completed)
 -   [2019](2019/README.md) (0% completed)
 -   [2020](2020/README.md) (20% completed)
--   [2021](2021/README.md) (64% completed)
+-   [2021](2021/README.md) (68% completed)