Course Schedule

Author: TonyKim9401

course-schedule/TonyKim9401.java

@@ -0,0 +1,37 @@
+// TC: O(n + p)
+// n -> number of courses, p -> the length of prerequisites
+// SC: O(n + m)
+// n -> the length of the graph size, m -> the length of nested list's size
+class Solution {
+    public boolean canFinish(int numCourses, int[][] prerequisites) {
+        List<List<Integer>> graph = new ArrayList<>();
+        int[] inDegree = new int[numCourses];
+
+        for (int i = 0; i < numCourses; i++) graph.add(new ArrayList<>());
+
+        for (int[] prerequisite : prerequisites) {
+            int course = prerequisite[0];
+            int pre = prerequisite[1];
+            graph.get(pre).add(course);
+            inDegree[course] += 1;
+        }
+
+        Queue<Integer> q = new LinkedList<>();
+        for (int i = 0; i < numCourses; i++) {
+            if (inDegree[i] == 0) q.offer(i);
+        }
+
+        int visitedCourses = 0;
+        while (!q.isEmpty()) {
+            int course = q.poll();
+            visitedCourses += 1;
+
+            for (int nextCourse : graph.get(course)) {
+                inDegree[nextCourse] -= 1;
+                if (inDegree[nextCourse] == 0) q.offer(nextCourse);
+            }
+        }
+
+        return visitedCourses == numCourses;
+    }
+}