[20250318] BOJ / ? / Дерево / 권혁준

Author: oncsr

khj20006/202503/18 BOJ ? Дерево.md

@@ -0,0 +1,87 @@
+```java
+
+import java.util.*;
+import java.io.*;
+
+class Main {
+	
+	// IO field
+	static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+	static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+	static StringTokenizer st = new StringTokenizer("");
+
+	static void nextLine() throws Exception {st = new StringTokenizer(br.readLine());}
+	static String nextToken() throws Exception {
+		if(!st.hasMoreTokens()) nextLine();
+		return st.nextToken();
+	}
+	static int nextInt() throws Exception { return Integer.parseInt(nextToken()); }
+	static long nextLong() throws Exception { return Long.parseLong(nextToken()); }
+	static void bwEnd() throws Exception {bw.flush();bw.close();}
+	
+	// Additional field
+	
+	static int N;
+	static List<Integer>[] V;
+	static int[] D;
+	static int ans = 0;
+	
+	public static void main(String[] args) throws Exception {
+		
+		ready();
+		solve();
+	
+		bwEnd();
+		
+	}
+	
+	static void ready() throws Exception{
+		
+		N = nextInt();
+		D = new int[N+1];
+		V = new List[N+1];
+		for(int i=1;i<=N;i++) V[i] = new ArrayList<>();
+		for(int i=1;i<N;i++) {
+			int a = nextInt(), b = nextInt();
+			V[a].add(b);
+			V[b].add(a);
+			D[a]++;
+			D[b]++;
+		}
+		
+	}
+	
+	static void solve() throws Exception{
+		
+		for(int i=1;i<=N;i++) if(D[i] > 3) {
+			bw.write("-1");
+			return;
+		}
+		
+		for(int i=1;i<=N;i++) {
+			if(D[i] == 2) {
+				dfs(i,0);
+				bw.write(ans + "\n");
+				return;
+			}
+		}
+		dfs(1,0);
+		bw.write(ans + "\n");
+
+	}
+	
+	static void dfs(int n, int p) {
+		if(D[n] == 0) return;
+		if(D[n] == 1) ans+=2;
+		if(D[n] == 2) ans++;
+		if(D[n] == 3) ans+=3;
+		D[n] = 0;
+		for(int i:V[n]) if(i != p) {
+			D[i]--;
+			dfs(i,n);
+		}
+	}
+	
+}
+
+```