[20260125] BOJ / G4 / 트리의 지름 / 이인희

LiiNi-coder/202601/25 BOJ 트리의 지름.md

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+```java
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Deque;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.w3c.dom.Node;
+
+public class Main{
+	private static int N;
+	private static Map<Integer, List<int[]>> Graph = new HashMap<Integer, List<int[]>>();
+	public static void main(String[] args) throws IOException {
+		BufferedReader br = new BufferedReader(new InputStreamReader(System.in ));
+		N = Integer.parseInt(br.readLine());
+		int t = N;
+		while(t-- > 1){
+			String[] tokens = br.readLine().split(" ");
+			int parent = Integer.parseInt(tokens[0] );
+			int child = Integer.parseInt(tokens[1]);
+			int weight = Integer.parseInt(tokens[2] );
+			Graph.putIfAbsent(parent, new ArrayList<int[]>());
+			Graph.get(parent).add(new int[]{child, weight});
+			Graph.putIfAbsent(child, new ArrayList<int[]>());
+			Graph.get(child).add(new int[]{parent, weight});
+		}
+		if(N == 1){
+			System.out.println(0);
+		}else{
+			int[] temp = bfs(1);
+			temp = bfs(temp[0]);
+			System.out.println(temp[1] );
+
+		}
+		br.close();
+	}
+
+	private static int[] bfs(int start) {
+		Deque<int[]> q = new ArrayDeque<int[]>();
+		boolean[] visited = new boolean[10_001];
+		visited[start] = true;
+		int maxDist = 0;
+		int nodeHavingMaxDist = 0;
+		q.offer(new int[]{start, 0});
+		while(!q.isEmpty()){
+			int[] qItem = q.poll();
+			int v = qItem[0];
+			int dist = qItem[1];
+			for(int[] nextInfo : Graph.get(v)){
+				int nv = nextInfo[0];
+				int weight = nextInfo[1];
+				if(visited[nv])
+					continue;
+				q.offer(new int[]{nv, dist + weight});
+				visited[nv] = true;
+			}
+			if (maxDist < dist) {
+				nodeHavingMaxDist = v;
+				maxDist = Math.max(maxDist, dist);
+			}
+		}
+		return new int[]{nodeHavingMaxDist, maxDist};
+	}
+}
+```