Submission #2374674

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Source Code Expand

public class Main {

  private static void solve() {
    int n = ni();
    int d = ni();
    int[] a = na(n);

    int mod = 1000000000 + 7;
    int max = 900;

    //c[i][j] = C(D-i,j)
    long[][] c = new long[max + 1][31];
    for (int i = 0; i <= max; i ++) {
      for (int j = 0; j <= 30; j ++) {
        long tmp = 1;
        
        for (int k = 0; k < j; k ++) {
          tmp *= (d - i - k);
          tmp %= mod;
          tmp *= invl(k + 1, mod);
          tmp %= mod;
        }
        c[i][j] = tmp;
      }
    }
    
    // dp[k][j] k個満たしてないものがある その合計はjである組み合わせ
    long[][] dp = new long[n + 1][max * 2];
    dp[0][0] = 1;
    for (int i = 0; i < n; i++) {
      for (int k = n - 1; k >= 0; k--) {
        for (int l = max; l >= 0; l--) {
          for (int j = 0; j < a[i]; j++) {
            dp[k + 1][j + l] += dp[k][l] * c[l][j] % mod;
            dp[k + 1][j + l] %= mod;
          }
        }
      }
    }

    long ret = 0;
    for (int k = 0; k <= n; k++) {
      for (int j = 0; j <= max; j++) {
        long now = powMod(n - k, d - j, mod) * dp[k][j] % mod;

        if (k % 2 == 0) {
          ret += now;
        } else {
          ret += mod - now;
        }
        ret %= mod;
      }
    }
    System.out.println(ret);
  }

  public static long powMod(long x, long k, long mod) {
    int n = 63 - Long.numberOfLeadingZeros(k);
    long answer = 1;
    for (int i = n; i >= 0; i--) {
      answer = (answer * answer) % mod;
      if (((k >> i) & 1L) == 1L) {
        answer = (answer * x) % mod;
      }
    }
    return answer;
  }

  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 = System.getProperty("debug");
        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));
  }
}

Submission Info

Judge Result