[20251211] BOJ / G4 / 트리의 지름 / 이종환

Author: 0224LJH

0224LJH/202512/11 BOJ 트리의 지름.md

@@ -0,0 +1,86 @@
+```java
+
+import java.util.StringTokenizer;
+import java.util.*;
+import java.io.*;
+
+public class Main {
+	
+	static int nodeCnt,ans = 0;
+	static Node[] nodes;
+	
+	static class Node{
+		int idx = 0;
+		Node parent = null;
+		HashSet<Node> set = new HashSet<>();
+		int dis = 0;
+		
+		public Node (int idx) {
+			this.idx = idx;
+		}
+	}
+
+	
+
+    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());
+    	nodes = new Node[nodeCnt+1];
+    	
+    	for (int i = 1; i<= nodeCnt; i++) {
+    		nodes[i] = new Node(i);
+    	}
+    	
+    	for (int i = 1; i < nodeCnt; i++) {
+    		StringTokenizer st = new StringTokenizer(br.readLine());
+    		int pNum = Integer.parseInt(st.nextToken());
+    		int cNum = Integer.parseInt(st.nextToken());
+    		int dis = Integer.parseInt(st.nextToken());
+    		Node p = nodes[pNum];
+    		Node c = nodes[cNum];
+    		c.parent = p;
+    		p.set.add(c);
+    		c.dis = dis;
+    	}
+    }
+    
+    private static void process() throws IOException {
+    	int rs = recursive(1);
+    	ans = Math.max(ans, rs);
+    	
+    }
+    
+    public static int recursive(int num) {
+    	Node target = nodes[num];
+    	if(target.set.isEmpty()) return target.dis;
+    	
+    	PriorityQueue<Integer> pq = new PriorityQueue<>(Collections.reverseOrder());
+    	
+    	for (Node n: target.set) {
+    		pq.add(recursive(n.idx));
+    	}
+    	int longest = pq.poll();
+    	
+    	if (!pq.isEmpty()) {
+    		int second = pq.poll();
+    		
+    		ans = Math.max(ans, longest+second);
+    	}
+    	
+    	
+    	return longest + target.dis;
+    }
+    
+   private static void print() {
+      System.out.println(ans);
+    }
+
+}
+```