pull-req for 524 (#531)

* fix for #524 hasGraphCycle

* add new task for someone else

.gitignore

@@ -2,4 +2,5 @@ dist
 node_modules
 npm-debug.log
 .DS_Store
-.idea
+.idea
+.vscode

lib/getMapKey.js

@@ -0,0 +1,7 @@
+// Write a function that get the nth key in the map
+// eg. Map([A,(object)][B,(object)][C,(object)][D,(object)]) -> get the third key in this map
+function getMapKey(map, n) {
+
+}
+
+module.exports = getMapKey;

lib/hasGraphCycle.js

@@ -13,11 +13,44 @@
 */
 
 // Given a directed graph, a character representing a start node,
-// and a character representing a destination, determine whether 
+// and a character representing a destination, determine whether
 // the graph contains a cycle
 
-function hasGraphCycle(graph){
-
+function hasGraphCycle(graph) {
+  //build an array of known nodes
+  var nodes = new Map();
+  //check all out-going nodes
+  graph.forEach(function (element) {
+    if (nodes.has(element.from)) {//node already known in map
+      nodes.get(element.from).links.push(element.to);
+    } else {//node not known
+      nodes.set(element.from, { visited: false, links: [] });
+      nodes.get(element.from).links.push(element.to);
+    }
+  });
+  //check nodes that are only in-going
+  graph.forEach(function (element) {
+    if (!nodes.has(element.to)) {//node already known in map
+      nodes.set(element.from, { visited: false, links: [] });
+    }
+  });
+  var first = nodes.keys().next().value;
+  //start with the first element of this list
+  var explorationList = [first];
+  var isCyclic = false;
+  nodes.get(first).visited = true;
+  while (explorationList.length > 0) {
+    var curr = explorationList.shift();
+    //parse through each nextNode of this current element
+    nodes.get(curr).links.forEach(function (child) {
+      if (!nodes.get(child).visited) {
+        nodes.get(child).visited = true;
+        explorationList.push(child);
+      } else {
+        isCyclic = true;
+      }
+    });
+  }
+  return isCyclic;
 }
-
 module.exports = hasGraphCycle;

test/getMapKey.test.js

@@ -0,0 +1,13 @@
+const { getMapKey } = require("../lib");
+describe("getMapKey", () => {
+  test("Get the third key of the given map.", () => {
+    var nodes = new Map();
+    nodes.set("A", { some: false, data: [] });
+    nodes.set("B", { some: false, data: [] });
+    nodes.set("C", { some: false, data: [] });
+    nodes.set("D", { some: false, data: [] });
+    nodes.set("E", { some: false, data: [] });
+    nodes.set("F", { some: false, data: [] });
+    expect(getMapKey(nodes,3)).toBe("C");
+  });
+});

test/hasGraphCycle.test.js

@@ -27,6 +27,6 @@ describe("hasGraphCycle", () => {
       {from: "D", to: "A"},
       {from: "E", to: "F"}
     ];
-    expect(hasGraphCycle(directedGraph)).toBe(true);
+    expect(hasGraphCycle(directedGraph)).toBe(false);
   });
 });