[20250905] BOJ / G3 / 사회망 서비스(SNS) / 김민진

zinnnn37/202509/5 BOJ G3 2533 사회망 서비스(SNS).md

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+```java
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.OutputStreamWriter;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.StringTokenizer;
+
+public class BJ_2533_사회망_서비스_SNS {
+
+    private static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    private static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    private static StringTokenizer st;
+
+    private static int N;
+    private static int[][] dp;  // [노드][0(일반인)/1(얼리어답터)]
+
+    private static boolean[] visited;
+    private static List<Integer>[] tree;
+
+    public static void main(String[] args) throws IOException {
+        init();
+        sol();
+    }
+
+    private static void init() throws IOException {
+        N = Integer.parseInt(br.readLine());
+
+        tree = new List[N + 1];
+        for (int i = 1; i <= N; i++) {
+            tree[i] = new ArrayList<>();
+        }
+
+        for (int i = 0; i < N - 1; i++) {
+            st = new StringTokenizer(br.readLine());
+
+            int u = Integer.parseInt(st.nextToken());
+            int v = Integer.parseInt(st.nextToken());
+
+            tree[u].add(v);
+            tree[v].add(u);
+        }
+        visited = new boolean[N + 1];
+        dp = new int[N + 1][2];
+    }
+
+    private static void sol() throws IOException {
+        find(1);
+
+        bw.write(Math.min(dp[1][0], dp[1][1]) + "");
+        bw.flush();
+        bw.close();
+        br.close();
+    }
+
+    private static void find(int u) {
+        visited[u] = true;
+        dp[u][0] = 1; // 초기화: 필요한 얼리어답터 수 = 1
+
+        for (int v : tree[u]) {
+            if (visited[v]) {
+                continue;
+            }
+            find(v);
+            dp[u][1] += dp[v][0]; // 내가 얼리어답터면 친구가 얼리어답터일 필요 없음
+            dp[u][0] += Math.min(dp[v][0], dp[v][1]);
+        }
+    }
+
+}
+```