BOJ_1043 : 거짓말

Author: spring0913

week8/BOJ_1043(거짓말).java

@@ -0,0 +1,72 @@
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    public static int[] parent;
+
+    public static void main(String[] args) throws IOException {
+        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];
+        for(int i=1; i<=N; i++) {
+            parent[i] = i;
+        }
+        st = new StringTokenizer(br.readLine());
+        int truthNum = Integer.parseInt(st.nextToken());
+        boolean[] truth = new boolean[N+1];
+        for(int i=0; i<truthNum; i++) {
+            int truthIndex = Integer.parseInt(st.nextToken());
+            truth[truthIndex] = true;
+        }
+        List<List<Integer>> attendee = new ArrayList<>();
+        for(int i=0; i<=M; i++) {
+            attendee.add(new ArrayList<>());
+        }
+        for(int i=1; i<=M; i++) {
+            st = new StringTokenizer(br.readLine());
+            int num = Integer.parseInt(st.nextToken());
+            for(int j=1; j<=num; j++) {
+                int attendeeIndex = Integer.parseInt(st.nextToken());
+                attendee.get(i).add(attendeeIndex);
+                union(attendee.get(i).get(0), attendeeIndex);
+            }
+        }
+        // 진실을 아는 사람의 parent 도 진실을 알도록 업데이트
+        for(int i=1; i<=N; i++) {
+            if(truth[i]) {
+                truth[find(i)] = true;
+            }
+        }
+
+        int answer = M;
+        for(int i=1; i<=M; i++) {
+            // 파티 참석자의 부모 노드가 진실을 아는 사람이면 거짓말 할 수 없음
+            for(int j=0; j<attendee.get(i).size(); j++) {
+                int attendeeParent = find(attendee.get(i).get(j));
+                if(truth[attendeeParent]) {
+                    answer--;
+                    break;
+                }
+            }
+        }
+        System.out.println(answer);
+    }
+
+    public static int find(int x) {
+        if(parent[x] == x) {
+            return x;
+        }
+        parent[x] = find(parent[x]);
+        return parent[x];
+    }
+    public static void union(int x, int y) {
+        x = find(x);
+        y = find(y);
+        if(x == y) {
+            return;
+        }
+        parent[y] = x;
+    }
+}