Add course-schedule solution

Author: Jeehay28

course-schedule/Jeehay28.js

@@ -0,0 +1,69 @@
+/**
+ * @param {number} numCourses
+ * @param {number[][]} prerequisites
+ * @return {boolean}
+ */
+
+// ✅ Graph DFS (Depth-First Search) approach
+// Time Complexity: O(V + E), where V is the number of courses (numCourses) and E is the number of prerequisites (edges).
+// Space Complexity: O(V + E), where V is the number of courses and E is the number of prerequisites.
+
+var canFinish = function (numCourses, prerequisites) {
+  // prerequisites = [
+  // [1, 0], // Course 1 depends on Course 0
+  // [2, 1], // Course 2 depends on Course 1
+  // [3, 1], // Course 3 depends on Course 1
+  // [3, 2]  // Course 3 depends on Course 2
+  // ];
+
+  // graph = {
+  // 0: [1], // Course 0 is a prerequisite for Course 1
+  // 1: [2, 3], // Course 1 is a prerequisite for Courses 2 and 3
+  // 2: [3], // Course 2 is a prerequisite for Course 3
+  // 3: [] // Course 3 has no prerequisites
+  // };
+
+  // Build the graph
+  const graph = {};
+
+  // for(let i=0; i<numCourses; i++) {
+  //     graph[i] = []
+  // }
+
+  // Fill in the graph with prerequisites
+  for (const [course, prereq] of prerequisites) {
+    if (!graph[prereq]) {
+      graph[prereq] = [];
+    }
+    graph[prereq].push(course);
+  }
+
+  const visited = new Array(numCourses).fill(0);
+
+  const dfs = (course) => {
+    if (visited[course] === 1) return false; // cycle detected!
+    if (visited[course] === 2) return true; // already visited
+
+    visited[course] = 1;
+
+    // // Visit all the courses that depend on the current course
+    for (const nextCourse of graph[course] || []) {
+      if (!dfs(nextCourse)) {
+        return false; // cycle detected!
+      }
+    }
+
+    visited[course] = 2; // fully visited and return true
+    return true;
+  };
+
+  // Check for each course whether it's possible to finish it
+  for (let i = 0; i < numCourses; i++) {
+    if (!dfs(i)) {
+      return false; // cycle detected!
+    }
+  }
+
+  return true; // no cycles
+};
+