[20251118] BOJ / G5 / 트리

Ukj0ng/202511/18 BOJ G5 트리.md

@@ -0,0 +1,70 @@
+```
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    private static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    private static final BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    private static List<Integer>[] edges;
+    private static int[] parent;
+    private static int N, M, answer;
+    public static void main(String[] args) throws IOException {
+        init();
+
+        for (int i = 0; i < N; i++) {
+            if (parent[i] == -1 && i != M) {
+                DFS(i);
+            }
+        }
+
+        bw.write(answer + "\n");
+        bw.flush();
+        bw.close();
+        br.close();
+    }
+
+    private static void init() throws IOException {
+        N = Integer.parseInt(br.readLine());
+
+        StringTokenizer st = new StringTokenizer(br.readLine());
+        parent = new int[N];
+        edges = new List[N];
+
+        for (int i = 0; i < N; i++) {
+            edges[i] = new ArrayList<>();
+        }
+
+        for (int i = 0; i < N; i++) {
+            parent[i] = Integer.parseInt(st.nextToken());
+            if (parent[i] == -1) continue;
+            edges[parent[i]].add(i);
+        }
+
+        M = Integer.parseInt(br.readLine());
+    }
+
+    private static void DFS(int start) {
+        if (isLeaf(start)) {
+            answer++;
+            return;
+        }
+
+        for (int next : edges[start]) {
+            if (next == M) continue;
+            DFS(next);
+        }
+    }
+
+    private static boolean isLeaf(int node) {
+        if (edges[node].isEmpty()) {
+            return true;
+        }
+
+        if (edges[node].size() == 1 && edges[node].get(0) == M) {
+            return true;
+        }
+
+        return false;
+    }
+}
+```