[20250922] BOJ / G4 / 문제 추천 시스템 Version 1 / 이강현

lkhyun/202509/22 BOJ G4 문제 추천 시스템 Version 1.md

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+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    static class Node{
+        int key,difficulty;
+
+        Node(int key, int difficulty){
+            this.key = key;
+            this.difficulty = difficulty;
+        }
+    }
+
+    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    static StringTokenizer st;
+    static int N,M;
+    static Map<Integer,Integer> problems = new HashMap<>();
+    static TreeSet<Node> s = new TreeSet<>((a,b) -> {
+        if(a.difficulty == b.difficulty){
+            return Integer.compare(a.key,b.key);
+        }else{
+            return Integer.compare(a.difficulty,b.difficulty);
+        }
+    });
+
+    public static void main(String[] args) throws IOException {
+        N = Integer.parseInt(br.readLine());
+        for (int i = 0; i < N; i++) {
+            st = new StringTokenizer(br.readLine());
+            int p = Integer.parseInt(st.nextToken());
+            int l = Integer.parseInt(st.nextToken());
+            problems.put(p,l);
+            s.add(new Node(p,l));
+        }
+
+        M = Integer.parseInt(br.readLine());
+        for (int i = 0; i < M; i++) {
+            st = new StringTokenizer(br.readLine());
+            String cmd = st.nextToken();
+
+            if(cmd.equals("add")){
+                int p = Integer.parseInt(st.nextToken());
+                int l = Integer.parseInt(st.nextToken());
+                problems.put(p,l);
+                s.add(new Node(p,l));
+            }
+            else if(cmd.equals("recommend")){
+                int x = Integer.parseInt(st.nextToken());
+                if(x == 1){
+                    Node hard = s.last();
+                    bw.write(hard.key + "\n");
+                }
+                else{
+                    Node easy = s.first();
+                    bw.write(easy.key + "\n");
+                }
+            }
+            else if(cmd.equals("solved")){
+                int p = Integer.parseInt(st.nextToken());
+                int difficulty = problems.get(p);
+                problems.remove(p);
+                s.remove(new Node(p, difficulty));
+            }
+        }
+
+        bw.close();
+    }
+}
+```