courses schedule

Author: eunhwa99

course-schedule/eunhwa99.java

@@ -0,0 +1,45 @@
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Queue;
+
+class Solution {
+
+  // TC: O(numCourses + E) E는 prerequisites 배열의 길이 (즉, 간선의 개수).
+  // SC: O(numCourses + E)
+  public boolean canFinish(int numCourses, int[][] prerequisites) {
+    int[] inDegree = new int[numCourses];
+    List<List<Integer>> adj = new ArrayList<>();
+
+    for (int i = 0; i < numCourses; i++) {
+      adj.add(new ArrayList<>());
+    }
+
+    for (int[] pre : prerequisites) {
+      adj.get(pre[1]).add(pre[0]);
+      inDegree[pre[0]]++;
+    }
+
+    Queue<Integer> queue = new LinkedList<>();
+    for (int i = 0; i < numCourses; i++) {
+      if (inDegree[i] == 0) {
+        queue.add(i);
+      }
+    }
+    for (int i = 0; i < numCourses; i++) {
+      if (queue.isEmpty()) {
+        return false;
+      }
+      int course = queue.poll();
+
+      for (int nextCourse : adj.get(course)) {
+        inDegree[nextCourse]--;
+        if (inDegree[nextCourse] == 0) {
+          queue.add(nextCourse);
+        }
+      }
+    }
+    return queue.isEmpty();
+  }
+}
+