[20250725] BOJ / G4 / 거짓말 / 이준희

JHLEE325/202507/25 BOJ G4 거짓말.md

@@ -0,0 +1,86 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    static int[] parent;
+    static boolean[] truth;
+
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringTokenizer st = new StringTokenizer(br.readLine());
+
+        int n = Integer.parseInt(st.nextToken());
+        int m = Integer.parseInt(st.nextToken());
+
+        parent = new int[n + 1];
+        truth = new boolean[n + 1];
+        for (int i = 1; i <= n; i++) parent[i] = i;
+
+        st = new StringTokenizer(br.readLine());
+        int t = Integer.parseInt(st.nextToken());
+        List<Integer> truthList = new ArrayList<>();
+        for (int i = 0; i < t; i++) {
+            int person = Integer.parseInt(st.nextToken());
+            truth[person] = true;
+            truthList.add(person);
+        }
+
+        List<List<Integer>> parties = new ArrayList<>();
+
+        for (int i = 0; i < m; i++) {
+            st = new StringTokenizer(br.readLine());
+            int cnt = Integer.parseInt(st.nextToken());
+            List<Integer> party = new ArrayList<>();
+
+            if (cnt > 0) {
+                int first = Integer.parseInt(st.nextToken());
+                party.add(first);
+                for (int j = 1; j < cnt; j++) {
+                    int next = Integer.parseInt(st.nextToken());
+                    union(first, next);
+                    party.add(next);
+                }
+            }
+            parties.add(party);
+        }
+
+        Set<Integer> truthRoots = new HashSet<>();
+        for (int i = 1; i <= n; i++) {
+            if (truth[i]) {
+                truthRoots.add(find(i));
+            }
+        }
+
+        int answer = 0;
+        for (List<Integer> party : parties) {
+            boolean canLie = true;
+            for (int person : party) {
+                if (truthRoots.contains(find(person))) {
+                    canLie = false;
+                    break;
+                }
+            }
+            if (canLie) answer++;
+        }
+
+        System.out.println(answer);
+    }
+
+    static int find(int x) {
+        if (x != parent[x]) {
+            parent[x] = find(parent[x]);
+        }
+        return parent[x];
+    }
+
+    static void union(int a, int b) {
+        int ra = find(a);
+        int rb = find(b);
+        if (ra != rb) {
+            parent[rb] = ra;
+        }
+    }
+}
+
+```