Merge pull request #1710 from AlgorithmWithGod/JHLEE325

[20251219] BOJ / G4 / Tree / 이준희

Author: ShinHeeEul

JHLEE325/202512/19 BOJ G4 Tree.md

@@ -0,0 +1,76 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+
+    static List<Integer>[] graph;
+    static boolean[] visited;
+    static boolean isgraph;
+
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringBuilder sb = new StringBuilder();
+
+        int T = Integer.parseInt(br.readLine());
+
+        for (int t=0;t<T;t++) {
+            StringTokenizer st;
+            int N = Integer.parseInt(br.readLine());
+            int M = Integer.parseInt(br.readLine());
+
+            graph = new ArrayList[N + 1];
+            visited = new boolean[N + 1];
+            isgraph = false;
+
+            for (int i = 1; i <= N; i++) {
+                graph[i] = new ArrayList<>();
+            }
+
+            for (int i = 0; i < M; i++) {
+                st = new StringTokenizer(br.readLine());
+                int a = Integer.parseInt(st.nextToken());
+                int b = Integer.parseInt(st.nextToken());
+
+                graph[a].add(b);
+                graph[b].add(a);
+            }
+
+            if (M != N - 1) {
+                sb.append("graph\n");
+                continue;
+            }
+
+            dfs(1, -1);
+
+            boolean connected = true;
+            for (int i = 1; i <= N; i++) {
+                if (!visited[i]) {
+                    connected = false;
+                    break;
+                }
+            }
+
+            if (isgraph || !connected) {
+                sb.append("graph\n");
+            } else {
+                sb.append("tree\n");
+            }
+        }
+
+        System.out.print(sb);
+    }
+
+    static void dfs(int cur, int parent) {
+        visited[cur] = true;
+
+        for (int next : graph[cur]) {
+            if (!visited[next]) {
+                dfs(next, cur);
+            } else if (next != parent) {
+                isgraph = true;
+            }
+        }
+    }
+}
+```