diff --git a/pom.xml b/pom.xml
index 0765296..0cba845 100644
--- a/pom.xml
+++ b/pom.xml
@@ -59,6 +59,19 @@
 			<artifactId>junit-jupiter</artifactId>
 			<scope>test</scope>
 		</dependency>
+
+        <dependency>
+            <groupId>org.eclipse.collections</groupId>
+            <artifactId>eclipse-collections-api</artifactId>
+            <version>13.0.0</version>
+			<scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.eclipse.collections</groupId>
+            <artifactId>eclipse-collections</artifactId>
+            <version>13.0.0</version>
+			<scope>test</scope>
+        </dependency>
     </dependencies>
 
     <profiles>
diff --git a/src/test/java/com/github/bibenga/alns/tsp/Tsp.java b/src/test/java/com/github/bibenga/alns/tsp/Tsp.java
index 9840741..568cb11 100644
--- a/src/test/java/com/github/bibenga/alns/tsp/Tsp.java
+++ b/src/test/java/com/github/bibenga/alns/tsp/Tsp.java
@@ -6,13 +6,15 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Comparator;
-import java.util.HashMap;
 import java.util.List;
-import java.util.Map;
 import java.util.Random;
 import java.util.random.RandomGenerator;
 import java.util.stream.IntStream;
 
+import org.eclipse.collections.api.map.primitive.IntIntMap;
+import org.eclipse.collections.impl.map.mutable.primitive.IntIntHashMap;
+import org.eclipse.collections.impl.set.mutable.primitive.IntHashSet;
+
 import com.github.bibenga.alns.ALNS;
 import com.github.bibenga.alns.State;
 import com.github.bibenga.alns.accept.HillClimbing;
@@ -29,7 +31,7 @@ public static void main(String[] args) throws Exception {
 
         Random rng = new Random(42);
 
-        TspState initSol = new TspState(nodes, new HashMap<>(), dists);
+        TspState initSol = new TspState(nodes, new IntIntHashMap(), dists);
         initSol = (TspState) greedyRepair(initSol, rng);
 
         System.out.println("optimal solution: 564");
@@ -248,7 +250,7 @@ private static State randomRemoval(State state, RandomGenerator rng) {
         int removed = 0;
         while (removed < toRemove) {
             int node = destroyed.nodes[rng.nextInt(destroyed.nodes.length)];
-            if (destroyed.edges.remove(node) != null) {
+            if (destroyed.edges.removeKeyIfAbsent(node, -1) != -1) {
                 removed++;
             }
         }
@@ -285,9 +287,11 @@ private static State worstRemoval(State state, RandomGenerator rng) {
     private static State greedyRepair(State state, RandomGenerator rng) {
         TspState cur = (TspState) state;
 
-        boolean[] visited = new boolean[cur.nodes.length];
-        for (int v : cur.edges.values())
-            visited[v] = true;
+        var visited = new IntHashSet();
+        for (var it = cur.edges.values().intIterator(); it.hasNext();) {
+            var v = it.next();
+            visited.add(v);
+        }
 
         int[] idx = IntStream.range(0, cur.nodes.length).toArray();
         shuffleArray(idx, rng);
@@ -306,21 +310,21 @@ private static State greedyRepair(State state, RandomGenerator rng) {
             if (node == -1)
                 throw new RuntimeException("node not found");
 
-            final int finalNode = node;
+            final int fNode = node;
             List<Integer> unvisited = new ArrayList<>();
             for (int other : cur.nodes) {
-                if (other != finalNode && !visited[other] && !wouldFormSubcycle(finalNode, other, cur))
+                if (other != fNode && !visited.contains(other) && !wouldFormSubcycle(fNode, other, cur))
                     unvisited.add(other);
             }
             if (unvisited.isEmpty())
                 throw new RuntimeException("unvisited is empty");
 
             int nearest = unvisited.stream()
-                    .min(Comparator.comparingDouble(a -> cur.dists[finalNode][a]))
+                    .min(Comparator.comparingDouble(a -> cur.dists[fNode][a]))
                     .orElseThrow();
 
             cur.edges.put(node, nearest);
-            visited[nearest] = true;
+            visited.add(nearest);
         }
         return cur;
     }
@@ -336,8 +340,8 @@ static void shuffleArray(int[] arr, RandomGenerator rnd) {
 
     private static boolean wouldFormSubcycle(int fromNode, int toNode, TspState state) {
         for (int step = 1; step < state.nodes.length; step++) {
-            Integer next = state.edges.get(toNode);
-            if (next == null)
+            int next = state.edges.getIfAbsent(toNode, -1);
+            if (next == -1)
                 return false;
             toNode = next;
             if (fromNode == toNode && step != state.nodes.length - 1)
@@ -346,7 +350,7 @@ private static boolean wouldFormSubcycle(int fromNode, int toNode, TspState stat
         return false;
     }
 
-    static void writeDotFile(String filename, double[][] coords, Map<Integer, Integer> edges) throws IOException {
+    static void writeDotFile(String filename, double[][] coords, IntIntMap edges) throws IOException {
         final double k = 3;
         double minX = Double.MAX_VALUE, minY = Double.MAX_VALUE;
         double maxX = -Double.MAX_VALUE, maxY = -Double.MAX_VALUE;
@@ -367,8 +371,9 @@ static void writeDotFile(String filename, double[][] coords, Map<Integer, Intege
                         "  %d [label=\"%d\", fontsize=48, pos=\"%f,%f!\", shape=circle, width=2, height=2, fixedsize=true];%n",
                         i, i, x, y);
             }
-            for (Map.Entry<Integer, Integer> e : edges.entrySet())
-                w.printf("  %d -> %d [arrowsize=4, penwidth=3];%n", e.getKey(), e.getValue());
+            edges.forEachKeyValue((key, value) -> {
+                w.printf("  %d -> %d [arrowsize=4, penwidth=3];%n", key, value);
+            });
             w.println("}");
         }
     }
diff --git a/src/test/java/com/github/bibenga/alns/tsp/TspState.java b/src/test/java/com/github/bibenga/alns/tsp/TspState.java
index a1f7e4b..b7b5b55 100644
--- a/src/test/java/com/github/bibenga/alns/tsp/TspState.java
+++ b/src/test/java/com/github/bibenga/alns/tsp/TspState.java
@@ -1,17 +1,17 @@
 package com.github.bibenga.alns.tsp;
 
-import java.util.HashMap;
-import java.util.Map;
+import org.eclipse.collections.api.map.primitive.MutableIntIntMap;
+import org.eclipse.collections.impl.map.mutable.primitive.IntIntHashMap;
 
 import com.github.bibenga.alns.State;
 
 class TspState implements State {
     final int[] nodes;
-    final Map<Integer, Integer> edges;
+    final MutableIntIntMap edges;
     final double[][] dists;
     private double objective = Double.NaN;
 
-    TspState(int[] nodes, Map<Integer, Integer> edges, double[][] dists) {
+    TspState(int[] nodes, MutableIntIntMap edges, double[][] dists) {
         this.nodes = nodes;
         this.edges = edges;
         this.dists = dists;
@@ -19,7 +19,7 @@ class TspState implements State {
 
     @Override
     public TspState clone() {
-        return new TspState(nodes, new HashMap<>(edges), dists);
+        return new TspState(nodes, new IntIntHashMap(edges), dists);
     }
 
     @Override