added java algorithms

Author: Morfly

src/java/.bazelrc

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+build --java_toolchain=@bazel_tools//tools/jdk:toolchain_java11 
+--host_java_toolchain=@bazel_tools//tools/jdk:toolchain_java11

src/java/Stub.java renamed to src/java/BUILD

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+workspace(name = "algorithms_java")

src/java/WORKSPACE

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+java_binary(
+    name = "bfs",
+    main_class = "sequential.graph.bfs.BreadthFirstTraversal",
+    srcs = glob(["*.java"]),
+)

src/java/sequential/graph/bfs/BUILD

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+package sequential.graph.bfs;
+
+import java.util.ArrayDeque;
+import java.util.Collection;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
+
+
+public class BreadthFirstTraversal {
+
+    public static <T> Collection<T> bfs(Map<T, List<T>> graph, T root) {
+        var explored = new LinkedHashSet<T>();
+        var searchQueue = new ArrayDeque<T>();
+
+        searchQueue.add(root);
+        while (!searchQueue.isEmpty()) {
+            var node = searchQueue.removeFirst();
+            if (!explored.contains(node)) {
+                explored.add(node);
+                searchQueue.addAll(graph.getOrDefault(node, List.of()));
+            }
+        }
+        return explored;
+    }
+
+
+    public static void main(String[] args) {
+        var graph = Map.of(
+                "you", List.of("alice", "bob", "clair"),
+                "alice", List.of("peggy"),
+                "clair", List.of("thom", "jonny"),
+                "bob", List.of("anuj", "paggy")
+        );
+
+        System.out.println(
+                bfs(graph, "you")
+        );
+    }
+}

src/java/sequential/graph/bfs/BreadthFirstTraversal.java

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+java_binary(
+    name = "dfs_iterative",
+    main_class = "sequential.graph.dfs.IterativeDepthFirstTraversal",
+    srcs = ["IterativeDepthFirstTraversal.java"],
+)
+
+java_binary(
+    name = "dfs_recursive",
+    main_class = "sequential.graph.dfs.RecursiveDepthFirstTraversal",
+    srcs = ["RecursiveDepthFirstTraversal.java"],
+)

src/java/sequential/graph/bfs/README.md

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+package sequential.graph.dfs;
+
+import java.util.ArrayDeque;
+import java.util.Collection;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
+
+
+public class IterativeDepthFirstTraversal {
+
+    public static <T> Collection<T> dfs(Map<T, List<T>> graph, T root) {
+        var searchStack = new ArrayDeque<T>();
+        var explored = new LinkedHashSet<T>();
+
+        searchStack.add(root);
+        while (!searchStack.isEmpty()) {
+            var node = searchStack.removeLast();
+            if (!explored.contains(node)) {
+                explored.add(node);
+                searchStack.addAll(graph.getOrDefault(node, List.of()));
+            }
+        }
+        return explored;
+    }
+
+
+    public static void main(String[] args) {
+        var graph = Map.of(
+                "you", List.of("alice", "bob", "clair"),
+                "alice", List.of("peggy"),
+                "clair", List.of("thom", "jonny"),
+                "bob", List.of("anuj", "paggy")
+        );
+
+        System.out.println(
+                dfs(graph, "you")
+        );
+    }
+}

src/java/sequential/graph/dfs/BUILD

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+package sequential.graph.dfs;
+
+import java.util.Collection;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+
+class RecursiveDepthFirstTraversal {
+
+    public static <T> Collection<T> dfs(Map<T, List<T>> graph, T root) {
+        var explored = new LinkedHashSet<T>();
+
+        explore(root, graph, explored);
+
+        return explored;
+    }
+
+    private static <T> void explore(T node, Map<T, List<T>> graph, Set<T> explored) {
+        explored.add(node);
+
+        var successors = graph.getOrDefault(node, List.of());
+        for (var succ : successors)
+            if (!explored.contains(succ)) explore(node, graph, explored);
+    }
+
+
+    public static void main(String[] args) {
+        var graph = Map.of(
+                "you", List.of("alice", "bob", "clair"),
+                "alice", List.of("peggy"),
+                "clair", List.of("thom", "jonny"),
+                "bob", List.of("anuj", "paggy")
+        );
+
+        System.out.println(
+                dfs(graph, "you")
+        );
+    }
+}