Merge pull request #664 from AlgorithmWithGod/lkhyun

[20250814] BOJ / G4 / 가르침 / 이강현

Author: ShinHeeEul

lkhyun/202508/14 BOJ G4 가르침.md

@@ -0,0 +1,87 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    static int N,K;
+    static boolean[] teach = new boolean[26];
+    static boolean[] shouldTeach = new boolean[26];
+    static int shouldTeachCnt;
+    static List<Set<Character>> words = new ArrayList<>();
+    static int ans = 0;
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+        StringTokenizer st = new StringTokenizer(br.readLine());
+        N = Integer.parseInt(st.nextToken());
+        K = Integer.parseInt(st.nextToken());
+
+        if(K < 5){
+            bw.write("0");
+            bw.close();
+            return;
+        }
+        K -= 5;
+        teach['a' - 'a'] = true;
+        teach['c' - 'a'] = true;
+        teach['i' - 'a'] = true;
+        teach['n' - 'a'] = true;
+        teach['t' - 'a'] = true;
+
+        
+
+        for (int i = 0; i < N; i++) {
+            String str = br.readLine();
+            Set<Character> temp = new HashSet<>();
+            for (int j = 4; j < str.length() - 4; j++) {
+                shouldTeach[str.charAt(j) - 'a'] = true;
+                temp.add(str.charAt(j));
+            }
+            words.add(temp);
+        }
+
+        for (int i = 0; i < shouldTeach.length; i++) {
+            if(shouldTeach[i] && !teach[i]) shouldTeachCnt++;
+        }
+
+        if(shouldTeachCnt <= K){
+            bw.write(N + "");
+            bw.close();
+            return;
+        }
+        
+        int startPoint = 1;
+        while(startPoint < 26 && (!shouldTeach[startPoint] || teach[startPoint])) startPoint++;
+        backTracking(startPoint, 0);
+        bw.write(ans+"");
+        bw.close();
+    }
+    static void backTracking(int start, int depth){
+        if(depth == K){
+            ans = Math.max(ans, canReadCount());
+            return;
+        }
+
+        for (int i = start; i < 26; i++) {
+            if(shouldTeach[i] && !teach[i]){
+                teach[i] = true;
+                backTracking(i+1, depth+1);
+                teach[i] = false;
+            }
+        }
+    }
+    static int canReadCount(){
+        int cnt = 0;
+        a: for (Set<Character> s : words) {
+            for (Character c : s) {
+                if(!teach[c - 'a']){
+                    continue a;
+                }
+            }
+            cnt++;
+        }
+        return cnt;
+    }
+    
+}
+```