[20250923] BOJ / G5 / 선수과목 / 이종환

0224LJH/202509/23 BOJ 선수과목.md

@@ -0,0 +1,92 @@
+```java
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.*;
+
+public class Main {
+
+	static int nodeCnt, preCnt,ans;
+	static Node[] nodes;;
+	static StringBuilder sb = new StringBuilder();
+
+
+	static class Node{
+		int semester;
+		int num;
+		int parentCnt;
+		HashSet<Node> children;
+
+		public Node(int num) {
+			semester = 1;
+			parentCnt = 0;
+			this.num = num;
+			children = new HashSet<>();
+
+		}
+	}
+
+    public static void main(String[] args) throws NumberFormatException, IOException {
+    	init();
+    	process();
+    	print();
+
+
+    }
+
+    public static void init() throws NumberFormatException, IOException {
+    	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    	StringTokenizer st = new StringTokenizer(br.readLine());
+    	nodeCnt = Integer.parseInt(st.nextToken());
+    	preCnt = Integer.parseInt(st.nextToken());
+    	nodes = new Node[nodeCnt+1];
+    	for (int i = 1; i <= nodeCnt; i++) {
+    		nodes[i] = new Node(i);
+    	}
+
+    	for (int i = 0; i < preCnt; i++) {
+    		st = new StringTokenizer(br.readLine());
+    		int parent = Integer.parseInt(st.nextToken());
+    		int child = Integer.parseInt(st.nextToken());
+
+    		nodes[parent].children.add(nodes[child]);
+    		nodes[child].parentCnt++;
+
+    	}
+
+    }
+
+    public static void process() { 	
+    	Queue<Node> pq = new LinkedList<>();
+
+    	for (int i = 1; i <= nodeCnt; i++ ) {
+
+    		Node node = nodes[i];
+    		if (node.parentCnt ==0) pq.add(node);
+
+    	}
+
+    	while (!pq.isEmpty()) {
+    		Node node = pq.poll();
+    		for (Node n: node.children ) {
+    			n.parentCnt--;
+    			if (n.parentCnt == 0) {
+    				n.semester = node.semester+1;
+    				pq.add(n);
+    			}
+    		}
+    	}
+
+
+    	for (int i = 1; i<= nodeCnt; i++) {
+    		sb.append(nodes[i].semester+ " ");
+    	}
+    }
+
+
+
+	public static void print() {
+		System.out.println(sb.toString());
+    }
+}
+```