modify code

大厂刷题班/class33/Problem_0210_CourseScheduleII.java

@@ -1,71 +1,40 @@
 package class33;
 
 import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.LinkedList;
-import java.util.Queue;
 
 public class Problem_0210_CourseScheduleII {
 
-	public static class Node {
-		public int name;
-		public int in;
-		public ArrayList<Node> nexts;
-
-		public Node(int n) {
-			name = n;
-			in = 0;
-			nexts = new ArrayList<>();
-		}
-	}
-
-	public int[] findOrder(int numCourses, int[][] prerequisites) {
-		int[] ans = new int[numCourses];
+	public static int[] findOrder(int numCourses, int[][] prerequisites) {
+		ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
 		for (int i = 0; i < numCourses; i++) {
-			ans[i] = i;
+			graph.add(new ArrayList<>());
 		}
-		if (prerequisites == null || prerequisites.length == 0) {
-			return ans;
-		}
-		HashMap<Integer, Node> nodes = new HashMap<>();
+		int[] indegree = new int[numCourses];
 		for (int[] arr : prerequisites) {
 			int to = arr[0];
 			int from = arr[1];
-			if (!nodes.containsKey(to)) {
-				nodes.put(to, new Node(to));
-			}
-			if (!nodes.containsKey(from)) {
-				nodes.put(from, new Node(from));
+			graph.get(from).add(to);
+			indegree[to]++;
 		}
-			Node t = nodes.get(to);
-			Node f = nodes.get(from);
-			f.nexts.add(t);
-			t.in++;
-		}
-		int index = 0;
-		Queue<Node> zeroInQueue = new LinkedList<>();
+		int[] zeroQueue = new int[numCourses];
+		int l = 0;
+		int r = 0;
 		for (int i = 0; i < numCourses; i++) {
-			if (!nodes.containsKey(i)) {
-				ans[index++] = i;
-			} else {
-				if (nodes.get(i).in == 0) {
-					zeroInQueue.add(nodes.get(i));
-				}
+			if (indegree[i] == 0) {
+				zeroQueue[r++] = i;
 			}
 		}
-		int needPrerequisiteNums = nodes.size();
 		int count = 0;
-		while (!zeroInQueue.isEmpty()) {
-			Node cur = zeroInQueue.poll();
-			ans[index++] = cur.name;
+		while (l < r) {
+			int cur = zeroQueue[l++];
 			count++;
-			for (Node next : cur.nexts) {
-				if (--next.in == 0) {
-					zeroInQueue.add(next);
+			for (int next : graph.get(cur)) {
+				if (--indegree[next] == 0) {
+					zeroQueue[r++] = next;
 				}
 			}
 		}
-		return count == needPrerequisiteNums ? ans : new int[0];
+		return count == numCourses ? zeroQueue : new int[0];
 	}
 
 }