week9 mission - Course Schedule

Author: dev-jonghoonpark

course-schedule/dev-jonghoonpark.md

@@ -0,0 +1,64 @@
+- 문제: https://leetcode.com/problems/course-schedule/
+- 풀이: https://algorithm.jonghoonpark.com/2024/03/01/leetcode-207
+
+```java
+public class Solution {
+	public boolean canFinish(int numCourses, int[][] prerequisites) {
+        if (prerequisites.length == 0) {
+            return true;
+        }
+
+		Map<Integer, Node> vertexMap = new HashMap<>();
+
+        for (int[] prerequisite : prerequisites) {
+            vertexMap.putIfAbsent(prerequisite[0], new Node(prerequisite[0]));
+            vertexMap.putIfAbsent(prerequisite[1], new Node(prerequisite[1]));
+
+            Node vertex1 = vertexMap.get(prerequisite[0]);
+            Node vertex2 = vertexMap.get(prerequisite[1]);
+
+            vertex1.edges.add(vertex2);
+            vertex2.reversedEdges.add(vertex1);
+        }
+
+        Deque<Integer> deque = new LinkedList<>();
+
+		int[] degrees = new int[numCourses];
+        for (int i = 0; i < degrees.length; i++) {
+            Node vertex = vertexMap.get(i);
+            if (vertex != null) {
+                degrees[i] = vertex.edges.size();
+                if (degrees[i] == 0) {
+                    deque.addLast(i);
+                }
+            }
+        }
+
+        while(!deque.isEmpty()) {
+            int vertexId = deque.removeFirst();
+            Node vertex = vertexMap.get(vertexId);
+            for (Node node : vertex.reversedEdges) {
+                degrees[node.id]--;
+                if (degrees[node.id] == 0) {
+                    deque.addLast(node.id);
+                }
+            }
+            vertexMap.remove(vertexId);
+        }
+
+        return vertexMap.isEmpty();
+	}
+}
+
+class Node {
+	int id;
+	List<Node> edges;
+    List<Node> reversedEdges;
+
+	public Node(int id) {
+		this.id = id;
+		edges = new ArrayList<>();
+        reversedEdges = new ArrayList<>();
+	}
+}
+```