From 766114c05bcd0b0388988aaf606e046857e6946a Mon Sep 17 00:00:00 2001
From: Pacien TRAN-GIRARD
Date: Tue, 10 May 2016 17:10:31 +0200
Subject: Add lists and maps functions

---
 src/ch/epfl/xblast/Lists.java      | 48 ++++++++++++++++++++++++++++++++++++++
 test/ch/epfl/xblast/ListsTest.java | 47 +++++++++++++++++++++++++++++++++----
 2 files changed, 91 insertions(+), 4 deletions(-)

diff --git a/src/ch/epfl/xblast/Lists.java b/src/ch/epfl/xblast/Lists.java
index cc6a1c8..bf0cafa 100644
--- a/src/ch/epfl/xblast/Lists.java
+++ b/src/ch/epfl/xblast/Lists.java
@@ -2,6 +2,7 @@ package ch.epfl.xblast;
 
 import java.util.*;
 import java.util.stream.Collectors;
+import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
 /**
@@ -181,4 +182,51 @@ public final class Lists {
                         .collect(Collectors.toList()));
     }
 
+    /**
+     * Maps linearly two lists.
+     *
+     * @param kl  the keys list
+     * @param vl  the values list
+     * @param <K> the key type
+     * @param <V> the value type
+     * @return the map
+     */
+    public static <K, V> Map<K, V> linearMap(List<K> kl, List<V> vl) {
+        if (Objects.isNull(kl) || Objects.isNull(vl) || kl.size() != vl.size())
+            throw new IllegalArgumentException();
+
+        return Collections.unmodifiableMap(IntStream
+                .range(0, kl.size()).mapToObj(i -> i)
+                .filter(i -> Objects.nonNull(vl.get(i)))
+                .collect(Collectors.toMap(kl::get, vl::get)));
+    }
+
+    /**
+     * Merges two maps Map<K1, IK> and Map<IK, V> -> Map<K1, V>.
+     *
+     * @param m1   key maps
+     * @param m2   values maps
+     * @param <K>  the keys type
+     * @param <IK> the intermediate keys type
+     * @param <V>  the values type
+     * @return the traversing map
+     */
+    public static <K, IK, V> Map<K, V> traverseMaps(Map<K, IK> m1, Map<IK, V> m2) {
+        return Collections.unmodifiableMap(m1.entrySet().stream()
+                .collect(Collectors.toMap(Map.Entry::getKey, e -> m2.get(e.getValue()))));
+    }
+
+    /**
+     * Returns an inverted copy of a bijective map.
+     *
+     * @param m   the map to invert
+     * @param <K> the keys type
+     * @param <V> the values type
+     * @return the inverted map
+     */
+    public static <K, V> Map<K, V> invertMap(Map<V, K> m) {
+        return Collections.unmodifiableMap(m.entrySet().stream()
+                .collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey)));
+    }
+
 }
diff --git a/test/ch/epfl/xblast/ListsTest.java b/test/ch/epfl/xblast/ListsTest.java
index b18b05e..e62eede 100644
--- a/test/ch/epfl/xblast/ListsTest.java
+++ b/test/ch/epfl/xblast/ListsTest.java
@@ -2,10 +2,7 @@ package ch.epfl.xblast;
 
 import org.junit.Test;
 
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.LinkedList;
-import java.util.List;
+import java.util.*;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 
@@ -63,4 +60,46 @@ public class ListsTest {
         assertEquals(expected, Lists.permutations(sampleList));
     }
 
+    @Test
+    public void areListsMapped() {
+        final List<Character> keyList = Arrays.asList('a', 'b');
+        final List<Integer> valueList = Arrays.asList(0, 1);
+
+        final Map<Character, Integer> expectedMap = new HashMap<>();
+        expectedMap.put('a', 0);
+        expectedMap.put('b', 1);
+
+        assertEquals(expectedMap, Lists.linearMap(keyList, valueList));
+    }
+
+    @Test
+    public void areMapsTraversed() {
+        final Map<Character, Integer> m1 = new HashMap<>();
+        m1.put('a', 0);
+        m1.put('b', 1);
+
+        final Map<Integer, String> m2 = new HashMap<>();
+        m2.put(0, "Apple");
+        m2.put(1, "Banana");
+
+        final Map<Character, String> expectedMap = new HashMap<>();
+        expectedMap.put('a', "Apple");
+        expectedMap.put('b', "Banana");
+
+        assertEquals(expectedMap, Lists.traverseMaps(m1, m2));
+    }
+
+    @Test
+    public void isMapInverted() {
+        final Map<Character, Integer> sampleMap = new HashMap<>();
+        sampleMap.put('a', 0);
+        sampleMap.put('b', 1);
+
+        final Map<Integer, Character> expectedMap = new HashMap<>();
+        expectedMap.put(0, 'a');
+        expectedMap.put(1, 'b');
+
+        assertEquals(expectedMap, Lists.invertMap(sampleMap));
+    }
+
 }
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