tdd-java-demo

commit f2284116e901134be3da6616a4291772fd2ea121
parent bff7df3fc7d6924cc4cd7da07bf226f5cf3c90a7
Author: Jul <jul@9o.is>
Date:   Wed, 31 Mar 2021 21:59:35 +0800

use multiset data structure to apply discounts to basket

Diffstat:
M
build.gradle
 | 
1
+
M
src/main/java/takehome/Discount.java
 | 
30
+++++++++++++++++++++---------

2 files changed, 22 insertions(+), 9 deletions(-)
diff --git a/build.gradle b/build.gradle
@@ -10,6 +10,7 @@ repositories {
 }
 
 dependencies {
+    compile 'com.google.guava:guava:30.1.1-jre'
     testImplementation 'org.junit.jupiter:junit-jupiter-api:5.6.0'
     testImplementation 'org.hamcrest:hamcrest:2.2'
     testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine'
diff --git a/src/main/java/takehome/Discount.java b/src/main/java/takehome/Discount.java
@@ -1,5 +1,9 @@
 package takehome;
 
+import com.google.common.collect.HashMultiset;
+import com.google.common.collect.Multiset;
+import com.google.common.collect.Multisets;
+
 import java.util.HashMap;
 import java.util.Map;
 
@@ -22,20 +26,28 @@ public class Discount {
         return amount;
     }
 
+    @SuppressWarnings("UnstableApiUsage")
     double getDiscount(Basket basket) {
-        Map<Item, Integer> frequencies = new HashMap<>();
+        Multiset<Item> basketSet = toMultiset(basket.getAmounts());
+        Multiset<Item> discountSet = toMultiset(items);
 
-        for (Item item : items.keySet()) {
-            int occurrences = basket.getAmount(item);
-            int requirement = items.get(item);
-            int frequency = Math.floorDiv(occurrences, requirement);
+        int occurrences = 0;
+        boolean occurrence = Multisets.containsOccurrences(basketSet, discountSet);
 
-            frequencies.put(item, frequency);
+        while (occurrence) {
+            occurrences++;
+            basketSet = Multisets.difference(basketSet, discountSet);
+            occurrence = Multisets.containsOccurrences(basketSet, discountSet);
         }
 
-        int frequency = frequencies.values()
-                .stream().reduce(Math::min).orElse(0);
+        return amount * occurrences;
+    }
 
-        return amount * frequency;
+    private Multiset<Item> toMultiset(Map<Item, Integer> map) {
+        Multiset<Item> multiset = HashMultiset.create();
+        for (Item item : map.keySet()) {
+            multiset.add(item, map.get(item));
+        }
+        return multiset;
     }
 }