[20250505] BOJ / G4 / 트리의 지름 / 이강현

lkhyun/202505/05 BOJ G4 트리의 지름.md

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+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    static class Node {
+        int to,cost;
+        Node(int to, int cost) {
+            this.to = to;
+            this.cost = cost;
+        }
+    }
+    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    static StringTokenizer st;
+    static int N;
+    static List<Node>[] adjList;
+
+    public static void main(String[] args) throws Exception {
+        N = Integer.parseInt(br.readLine());
+        if(N == 1){
+            bw.write("0");
+            bw.close();
+            return;
+        }
+        adjList = new ArrayList[N+1];
+        for (int i = 1; i <= N; i++) {
+            adjList[i] = new ArrayList<>();
+        }
+        for (int i = 1; i < N; i++) {
+            st = new StringTokenizer(br.readLine());
+            int p = Integer.parseInt(st.nextToken());
+            int c = Integer.parseInt(st.nextToken());
+            int w = Integer.parseInt(st.nextToken());
+            adjList[p].add(new Node(c, w));
+            adjList[c].add(new Node(p, w));
+        }
+        int[] dist = new int[N+1];
+        int A = BFS(1,dist);
+        int B = BFS(A,dist);
+        bw.write(dist[B]+"");
+        bw.close();
+    }
+    public static int BFS(int start,int[] dist){
+        Arrays.fill(dist, Integer.MAX_VALUE);
+        Queue<Integer> q = new ArrayDeque<>();
+        q.add(start);
+        dist[start] = 0;
+
+        int destination = start;
+        while(!q.isEmpty()){
+            int cur = q.poll();
+            for(Node node : adjList[cur]){
+                if(dist[node.to] == Integer.MAX_VALUE){
+                    dist[node.to] = dist[cur] + node.cost;
+                    q.add(node.to);
+                    if(dist[node.to] > dist[destination]) destination = node.to;
+                }
+            }
+        }
+        return destination;
+    }
+}
+```