[20251208] BOJ / G5 / 트리 / 이종환

0224LJH/202512/08 BOJ 트리.md

@@ -0,0 +1,75 @@
+```java
+
+import java.util.StringTokenizer;
+import java.util.*;
+import java.io.*;
+
+public class Main {
+
+	static int nodeCnt,ans;
+	static Node[] nodes;
+	static Node root;
+
+   static class Node {
+	   Node parent;
+	   boolean alive = true;
+	   Set<Node> children = new HashSet<>();
+
+	   public void checkLeaf() {
+		   int childCnt = 0;
+		   for (Node n: children) {
+			   if (!n.alive) continue;
+			   childCnt++;
+			   n.checkLeaf();
+		   }
+		   if (childCnt==0) ans++;
+	   }
+
+   }
+
+
+    public static void main(String[] args) throws IOException {
+    	init();
+    	process();
+    	print();
+
+    }
+
+    private static void init() throws IOException{
+    	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    	nodeCnt = Integer.parseInt(br.readLine());
+    	ans = 0;
+
+    	nodes = new Node[nodeCnt];
+    	for (int i = 0; i < nodeCnt; i++) {
+    		nodes[i] = new Node();
+    	}
+    	StringTokenizer st = new StringTokenizer(br.readLine());
+    	for (int i = 0; i < nodeCnt; i++) {
+    		int parent = Integer.parseInt(st.nextToken());
+    		if (parent == -1) {
+    			root = nodes[i];
+    			continue;
+    		}
+    		Node p = nodes[parent];
+    		nodes[i].parent = p;
+    		p.children.add(nodes[i]);
+    	}
+
+    	int targetNum = Integer.parseInt(br.readLine());
+    	Node target = nodes[targetNum];
+    	target.alive = false;
+
+    }
+
+    private static void process() throws IOException {
+    	if (root.alive) root.checkLeaf();
+
+    }
+
+   private static void print() {
+      System.out.println(ans);
+    }
+
+}
+```