207 course schedule

anthonysim · anthonysim · commit c02bd1451f4e · 2022-07-06T16:48:51.000-07:00
diff --git a/javascript/207-canFinish.js b/javascript/207-canFinish.js
@@ -0,0 +1,38 @@
+function createGraph(numCourses, edges) {
+  const graph = Array.from({ length: numCourses }, () => []);
+
+  for (let edge of edges) {
+    let [a, b] = edge;
+
+    if (!(a in graph)) graph[a] = [];
+    if (!(b in graph)) graph[b] = [];
+
+    graph[a].push(b);
+  }
+  return graph;
+}
+
+function canFinish(numCourses, preq) {
+  const graph = createGraph(numCourses, preq);
+  let seen = new Set();
+  let seeing = new Set();
+
+  function explore(course) {
+    if (seen.has(course)) return true;
+    if (seeing.has(course)) return false;
+
+    seeing.add(course);
+    for (let neighbor of graph[course]) {
+      if (!explore(neighbor)) return false;
+    }
+
+    seen.add(course);
+    seeing.delete(course);
+    return true;
+  }
+
+  for (let i = 0; i < numCourses; i++) {
+    if (!explore(i)) return false;
+  }
+  return true;
+};
