結果

問題 No.758 VVVVV
ユーザー hiromi_ayase
提出日時 2018-12-07 13:50:53
言語 Java
(openjdk 23)
結果
AC  
実行時間 285 ms / 2,000 ms
コード長 3,417 bytes
コンパイル時間 2,385 ms
コンパイル使用メモリ 86,040 KB
実行使用メモリ 47,696 KB
最終ジャッジ日時 2024-10-14 01:46:33
合計ジャッジ時間 8,150 ms
ジャッジサーバーID
（参考情報） 		judge3 / judge2
このコードへのチャレンジ
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ファイルパターン 結果
sample AC * 3
other AC * 23
権限があれば一括ダウンロードができます

ソースコード

diff # 

public class Main {
  private static void solve() {

     int n = ni();
     if (n == 1) {
       System.out.println(1);
       return;
     }
     int[] cnt = new int[n];
     for (int i = 0; i < n-1; i ++) {
       cnt[ni() - 1] ++;
       cnt[ni() - 1] ++;
     }
     int leaf = 0;
     for (int i = 1; i < n; i ++) {
       if (cnt[i] == 1) leaf ++;
     }
     
     int mod = 1000000000 + 7;
     
     long ret = c(n - 1, leaf - 1, mod) * c(n - 2, leaf - 1, mod) % mod;
     ret = ret * invl(leaf, mod) % mod;
     System.out.println(ret);
  }
  
  private static long c(int n, int r, int mod) {
    long x = 1;
    long y = 1;
    for (int i = 0; i < r; i ++) {
      x *= n - i;
      y *= i + 1;
      x %= mod;
      y %= mod;
    }
    return x * invl(y, mod) % mod;
  }

  public static long invl(long a, long mod) {
    long b = mod;
    long p = 1, q = 0;
    while (b > 0) {
        long c = a / b;
        long d;
        d = a;
        a = b;
        b = d % b;
        d = p;
        p = q;
        q = d - c * q;
    }
    return p < 0 ? p + mod : p;
}
  
  public static void main(String[] args) {
    new Thread(null, new Runnable() {
      @Override
      public void run() {
        long start = System.currentTimeMillis();
        String debug = args.length > 0 ? args[0] : null;
        if (debug != null) {
          try {
            is = java.nio.file.Files.newInputStream(java.nio.file.Paths.get(debug));
          } catch (Exception e) {
            throw new RuntimeException(e);
          }
        }
        reader = new java.io.BufferedReader(new java.io.InputStreamReader(is), 32768);
        solve();
        out.flush();
        tr((System.currentTimeMillis() - start) + "ms");
      }
    }, "", 64000000).start();
  }

  private static java.io.InputStream is = System.in;
  private static java.io.PrintWriter out = new java.io.PrintWriter(System.out);
  private static java.util.StringTokenizer tokenizer = null;
  private static java.io.BufferedReader reader;

  public static String next() {
    while (tokenizer == null || !tokenizer.hasMoreTokens()) {
      try {
        tokenizer = new java.util.StringTokenizer(reader.readLine());
      } catch (Exception e) {
        throw new RuntimeException(e);
      }
    }
    return tokenizer.nextToken();
  }

  private static double nd() {
    return Double.parseDouble(next());
  }

  private static long nl() {
    return Long.parseLong(next());
  }

  private static int[] na(int n) {
    int[] a = new int[n];
    for (int i = 0; i < n; i++)
      a[i] = ni();
    return a;
  }

  private static char[] ns() {
    return next().toCharArray();
  }

  private static long[] nal(int n) {
    long[] a = new long[n];
    for (int i = 0; i < n; i++)
      a[i] = nl();
    return a;
  }

  private static int[][] ntable(int n, int m) {
    int[][] table = new int[n][m];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[i][j] = ni();
      }
    }
    return table;
  }

  private static int[][] nlist(int n, int m) {
    int[][] table = new int[m][n];
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        table[j][i] = ni();
      }
    }
    return table;
  }

  private static int ni() {
    return Integer.parseInt(next());
  }

  private static void tr(Object... o) {
    if (is != System.in)
      System.out.println(java.util.Arrays.deepToString(o));
  }
}
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