[20250915] BOJ / G2 / 문제집 / 이종환

0224LJH/202509/15 BOJ 문제집.md

@@ -0,0 +1,83 @@
+```java
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.*;
+
+public class Main {
+	static int nodeCnt, infoCnt;
+	static Node[] nodes;
+	static StringBuilder sb = new StringBuilder();
+	static class Node implements Comparable<Node>{
+		int num;
+		int beforeCnt = 0; // 이 노드 전에 나와야 하는 노드 수
+		HashSet<Node> after = new HashSet<>();
+
+
+
+		public Node(int num) {
+			this.num = num;
+		}
+
+		@Override
+		public int compareTo(Node n) {
+			return Integer.compare(this.num, n.num);
+		}
+	}
+
+
+    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());
+    	infoCnt = 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 < infoCnt; i++) {
+    		st = new StringTokenizer(br.readLine());
+    		int before = Integer.parseInt(st.nextToken());
+    		int after = Integer.parseInt(st.nextToken());
+
+    		nodes[after].beforeCnt++;
+    		nodes[before].after.add(nodes[after]);
+    	}
+
+    }
+
+    public static void process() {   
+    	PriorityQueue<Node> pq = new PriorityQueue<>();
+    	for (int i = 1; i<= nodeCnt; i++) {
+    		if (nodes[i].beforeCnt != 0 )continue;
+    		pq.add(nodes[i]);
+    	}
+
+    	while(!pq.isEmpty()) {
+    		Node n =pq.poll();
+    		if ( n.beforeCnt != 0) {
+    			pq.add(n);
+    			continue;
+    		}
+
+    		sb.append(n.num).append(" ");
+
+    		for (Node b: n.after) {
+    			b.beforeCnt--;
+    			if (b.beforeCnt == 0) pq.add(b);
+    		}
+    	}
+
+    }
+
+
+	public static void print() {
+    	System.out.println(sb.toString());
+    }
+}
+```