Refactor DesignParkingSystem1603: move to proper package structure and add tests

src/main/java/com/leetcode/easy/DesignParkingSystem1603.java

@@ -0,0 +1,25 @@
+// Tags: Design, Simulation, Counting
+package com.leetcode.easy;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class DesignParkingSystem1603 {
+    private final Map<Integer, Integer> spaces = new HashMap<>();
+
+    public DesignParkingSystem1603(int big, int medium, int small) {
+        this.spaces.put(1, big);
+        this.spaces.put(2, medium);
+        this.spaces.put(3, small);
+    }
+
+    public boolean addCar(int carType) {
+        int remaining = this.spaces.get(carType);
+        if (remaining == 0) {
+            return false;
+        }
+        this.spaces.put(carType, remaining - 1);
+        return true;
+
+    }
+}

src/test/java/com/leetcode/easy/DesignParkingSystem1603Test.java

@@ -0,0 +1,23 @@
+package com.leetcode.easy;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class DesignParkingSystem1603Test {
+
+    @Test
+    void testAddCar_Example1() {
+        DesignParkingSystem1603 parkingSystem = new DesignParkingSystem1603(1, 1, 0);
+
+        boolean result1 = parkingSystem.addCar(1); // big car - true
+        boolean result2 = parkingSystem.addCar(2); // medium car - true
+        boolean result3 = parkingSystem.addCar(3); // small car - false (no slots)
+        boolean result4 = parkingSystem.addCar(1); // big car - false (already occupied)
+
+        assertTrue(result1);
+        assertTrue(result2);
+        assertFalse(result3);
+        assertFalse(result4);
+    }
+}