BOJ_2533 : 사회망 서비스

Author: spring0913

week13/BOJ_2533(사회망 서비스).java

@@ -0,0 +1,47 @@
+import java.io.*;
+import java.util.*;
+
+public class Main {
+
+    private static boolean[] visited;
+    private static int N;
+    private static int[][] d;
+    private static List<List<Integer>> tree;
+
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        N = Integer.parseInt(br.readLine());
+        d = new int[N+1][2];
+        tree = new ArrayList<>();
+        visited = new boolean[N+1];
+        for(int i=0; i<=N; i++) {
+            tree.add(new ArrayList<>());
+            d[i][1] = 1;
+        }
+        for(int i=0; i<N-1; i++) {
+            StringTokenizer st = new StringTokenizer(br.readLine());
+            int v1 = Integer.parseInt(st.nextToken());
+            int v2 = Integer.parseInt(st.nextToken());
+            tree.get(v1).add(v2);
+            tree.get(v2).add(v1);
+        }
+        // d[i][0] : i 노드가 얼리어답터가 아닌 경우의 최소 얼리어답터 수
+        // d[i][1] : i 노드가 얼리어답터인 경우의 최소 얼리어답터 수
+        visited[1] = true;
+        dfs(1);
+        System.out.println(Math.min(d[1][0], d[1][1]));
+    }
+
+    public static void dfs(int n) {
+        List<Integer> child = tree.get(n);
+        for(int i=0; i<child.size(); i++) {
+            int next = child.get(i);
+            if(!visited[next]) {
+                visited[next] = true;
+                dfs(next);
+                d[n][0] += d[next][1];
+                d[n][1] += Math.min(d[next][0], d[next][1]);
+            }
+        }
+    }
+}