[20251027] BOJ / G5 / 트리 / 김수연

suyeun84/202510/27 BOJ G5 트리.md

@@ -0,0 +1,56 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class boj1068 {
+    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    static StringTokenizer st;
+    static void nextLine() throws Exception {st = new StringTokenizer(br.readLine());}
+    static int nextInt() {return Integer.parseInt(st.nextToken());}
+
+    public static void main(String[] args) throws Exception {
+        nextLine();
+        int N = nextInt();
+        int answer = 0;
+        ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
+        nextLine();
+        for (int i = 0; i < N; i++) graph.add(new ArrayList<Integer>());
+        for (int i = 0; i < N; i++) {
+            int par = nextInt();
+            if (par == -1) continue;
+            graph.get(par).add(i); // 부모에 자식 연결
+        }
+        nextLine();
+        int remove = nextInt();
+        boolean[] poss = new boolean[N];
+        Arrays.fill(poss, true);
+        Queue<Integer> q = new LinkedList<>();
+        poss[remove] = false;
+        for (int n : graph.get(remove)) {
+            q.add(n);
+            poss[n] = false;
+        }
+        while (!q.isEmpty()) {
+            int node = q.poll();
+            for (int ne : graph.get(node)) {
+                if (!poss[ne]) continue;
+                q.add(ne);
+                poss[ne] = false;
+            }
+        }
+        for (int i = 0; i < N; i++) {
+            boolean flag = false;
+            if (!poss[i]) continue;
+            for (int p : graph.get(i)) {
+                if (poss[p]) {
+                    flag = true;
+                    break;
+                }
+            }
+            if (graph.get(i).isEmpty()) flag = false;
+            if (!flag) answer++;
+        }
+        System.out.println(answer);
+    }
+}
+```