Support case of disconnected subgraphs

Author: curran

index.js

@@ -245,7 +245,9 @@ module.exports = function Graph(serialized){
         }
       });
       if (minNode === undefined) {
-        throw new Error("No path exists.");
+        // If we reach here, there's a disconnected subgraph, and we're done.
+        q = {};
+        return null;
       }
       delete q[minNode];
       return minNode;
@@ -279,7 +281,10 @@ module.exports = function Graph(serialized){
         nodeList.push(node);
         node = p[node];
       }
-      nodeList.push(source);
+      if (node !== source) {
+        throw new Error("No path found");
+      }
+      nodeList.push(node);
       nodeList.reverse();
       return nodeList;
     }

test.js

@@ -378,6 +378,14 @@ describe("Graph", function() {
         .addEdge("d", "e");
       assert.throws(() => graph.shortestPath("a", "e"), /No path/);
     });
+
+    it("Should be robust to disconnected subgraphs.", function (){
+      var graph = Graph()
+        .addEdge("a", "b")
+        .addEdge("b", "c")
+        .addEdge("d", "e");
+      assert.deepEqual(graph.shortestPath("a", "c"), ["a", "b", "c"]);
+    });
   });
 });