Add BreadthFirstSearch

Author: rabestro

src/main/java/algorithm/BreadthFirstSearch.java

@@ -0,0 +1,36 @@
+package algorithm;
+
+import java.util.*;
+
+import static java.util.function.Predicate.not;
+import static java.util.stream.Stream.iterate;
+
+public class BreadthFirstSearch<T> implements Algorithm<T> {
+    @Override
+    public List<T> findPath(Graph<T> graph, T source, T target) {
+        final var queue = new LinkedList<T>();
+
+        final var visited = new HashSet<T>();
+        final var previous = new HashMap<T, T>();
+
+        queue.add(source);
+
+        while (!queue.isEmpty()) {
+            final var node = queue.pollFirst();
+            if (target.equals(node)) {
+                final var path = new LinkedList<T>();
+                iterate(node, Objects::nonNull, previous::get).forEach(path::addFirst);
+                return path;
+            }
+            visited.add(node);
+            graph.nodes().get(node).keySet().stream()
+                    .filter(not(visited::contains))
+                    .forEach(it -> {
+                        previous.put(it, node);
+                        queue.add(it);
+                    });
+        }
+        return new LinkedList<>();
+    }
+
+}

src/main/java/algorithm/Dijkstras.java

@@ -12,6 +12,7 @@ public List<T> findPath(Graph<T> graph, T source, T target) {
         final var distances = new HashMap<T, Double>();
         final var previous = new HashMap<T, T>();
         queue.add(source);
+        distances.put(source, .0);
 
         while (!queue.isEmpty()) {
             final var prev = queue.pollFirst();

src/test/groovy/algorithm/BreadthFirstSearchSpec.groovy

@@ -0,0 +1,36 @@
+package algorithm
+
+import spock.lang.Specification
+import spock.lang.Subject
+import spock.lang.Unroll
+
+class BreadthFirstSearchSpec extends Specification {
+    @Subject
+    def algorithm = new BreadthFirstSearch()
+
+    @Unroll("from #source to #target the time is #time and the path is #expected")
+    def 'should find a route for sample one'() {
+        given:
+        def graph = new Graph([
+                A: [B: 7, C: 2],
+                B: [A: 3, C: 5],
+                C: [A: 1, B: 3]
+        ])
+
+        when:
+        def path = algorithm.findPath(graph, source, target)
+
+        then:
+        path == expected
+
+        and:
+        graph.getDistance(path) == time as double
+
+        where:
+        source | target || time | expected
+        'A'    | 'A'    || 0    | ['A']
+        'A'    | 'B'    || 7    | ['A', 'B']
+        'B'    | 'C'    || 5    | ['B', 'C']
+    }
+
+}