feat: update structure

cs2030s/labs/PE2 2021-2022/Query.java

@@ -0,0 +1,33 @@
+
+/**
+ * CS2030S PE1 Question 2
+ * AY21/22 Semester 2
+ *
+ * @author A0000000X
+ */
+import java.util.Map;
+import java.util.List;
+import java.util.stream.Stream;
+import java.util.function.Predicate;
+
+class Query {
+
+    public static <T, S> Stream<Map.Entry<T, S>> getFilteredByKey(Map<T, S> table, Predicate<T> p) {
+        return table.entrySet().stream().filter(e -> p.test(e.getKey()));
+    }
+
+    public static Stream<Integer> getIdsFromName(Map<String, List<Integer>> table, String name) {
+        return getFilteredByKey(table, s -> s.equals(name)).flatMap(e -> e.getValue().stream());
+    }
+
+    public static Stream<Double> getCostsFromIDs(Map<Integer, Double> table, Stream<Integer> ids) {
+        return ids.flatMap(id -> getFilteredByKey(table, e -> e == id).map(e -> e.getValue()));
+    }
+
+    public static Stream<String> allCustomerCosts(Map<String, List<Integer>> customerTable,
+            Map<Integer, Double> salesTable) {
+        return customerTable.entrySet()
+                .stream()
+                .flatMap(e -> e.getValue().stream().map(p -> e.getKey() + ": " + p));
+    }
+}