[20251025] BOJ / G5 / 트리 / 이준희

JHLEE325/202510/25 BOJ G5 트리.md

@@ -0,0 +1,62 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    static int N;
+    static int dnode;
+    static List<Integer>[] tree;
+    static boolean[] visited;
+    static int leafcount = 0;
+    static int root;
+
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        N = Integer.parseInt(br.readLine());
+        tree = new ArrayList[N];
+        visited = new boolean[N];
+        for (int i = 0; i < N; i++) {
+            tree[i] = new ArrayList<>();
+        }
+
+        StringTokenizer st = new StringTokenizer(br.readLine());
+        root = -1;
+        for (int i = 0; i < N; i++) {
+            int parent = Integer.parseInt(st.nextToken());
+            if (parent == -1) {
+                root = i;
+            } else {
+                tree[parent].add(i);
+            }
+        }
+
+        dnode = Integer.parseInt(br.readLine());
+
+        if (dnode == root) {
+            System.out.println(0);
+            return;
+        }
+
+        dfs(root);
+        System.out.println(leafcount);
+    }
+
+    static void dfs(int now) {
+        visited[now] = true;
+        int childCount = 0;
+
+        for (int next : tree[now]) {
+            if (next == dnode) continue;
+            if (!visited[next]) {
+                dfs(next);
+                childCount++;
+            }
+        }
+
+        if (childCount == 0) {
+            leafcount++;
+        }
+    }
+}
+
+```