java: add «874. Walking Robot Simulation»

Signed-off-by: Matej Focko <me@mfocko.xyz>

java/walking-robot-simulation.java

@@ -0,0 +1,57 @@
+import java.util.HashSet;
+
+class Solution {
+  private static final int TURN_LEFT = -2;
+  private static final int TURN_RIGHT = -1;
+
+  private record Vec(int x, int y) {
+    public Vec turnLeft() {
+      return new Vec(-y, x);
+    }
+
+    public Vec turnRight() {
+      return new Vec(y, -x);
+    }
+
+    public Vec add(Vec other) {
+      return new Vec(x + other.x, y + other.y);
+    }
+
+    public int distance() {
+      return Math.abs(x * x + y * y);
+    }
+  }
+
+  public int robotSim(int[] commands, int[][] obstacles) {
+    int maxDistance = 0;
+
+    // Process obstacles
+    var uniqueObstacles = new HashSet<Vec>();
+    for (int[] obstacle : obstacles) {
+      uniqueObstacles.add(new Vec(obstacle[0], obstacle[1]));
+    }
+
+    var pos = new Vec(0, 0);
+    var direction = new Vec(0, 1);
+
+    for (int command : commands) {
+      if (command == TURN_LEFT) {
+        direction = direction.turnLeft();
+      } else if (command == TURN_RIGHT) {
+        direction = direction.turnRight();
+      }
+
+      for (var steps = 0; steps < command; ++steps) {
+        var next = pos.add(direction);
+        if (uniqueObstacles.contains(next)) {
+          break;
+        }
+
+        pos = next;
+        maxDistance = Math.max(maxDistance, pos.distance());
+      }
+    }
+
+    return maxDistance;
+  }
+}