Minimum scalar product

Main.java

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.Random;
import java.io.IOException;
import java.io.InputStream;

/**
 * Built using CHelper plug-in Actual solution is at the top
 *
 * @author MaxHeap
 */
public class Main {

  public static void main(String[] args) {
    InputStream inputStream = System.in;
    OutputStream outputStream = System.out;
    InputReader in = new InputReader(inputStream);
    PrintWriter out = new PrintWriter(outputStream);
    MinimumScalarProduct solver = new MinimumScalarProduct();
    int testCount = Integer.parseInt(in.next());
    for (int i = 1; i <= testCount; i++) {
      solver.solve(i, in, out);
    }
    out.close();
  }

  static class MinimumScalarProduct {

    public void solve(int testNumber, InputReader in, PrintWriter out) {
      int n = in.nextInt();
      long[] a = in.nextLongArray(n);
      long[] b = in.nextLongArray(n);
      ArrayUtils.sort(a);
      ArrayUtils.sort(b);
      ArrayUtils.reverse(b);
      long ans = 0;
      for (int i = 0; i < n; i++) {
        ans += a[i] * b[i];
      }
      out.println("Case #" + testNumber + ": " + ans);
    }

  }

  static class InputReader {

    private InputStream stream;
    private byte[] buf = new byte[1 << 13];
    private int curChar;
    private int numChars;

    public InputReader(InputStream stream) {
      this.stream = stream;
    }

    public int read() {
      if (this.numChars == -1) {
        throw new UnknownError();
      } else {
        if (this.curChar >= this.numChars) {
          this.curChar = 0;

          try {
            this.numChars = this.stream.read(this.buf);
          } catch (IOException ex) {
            throw new InputMismatchException();
          }

          if (this.numChars <= 0) {
            return -1;
          }
        }

        return this.buf[this.curChar++];
      }
    }

    public int nextInt() {
      int c;
      for (c = this.read(); isSpaceChar(c); c = this.read()) {
      }

      byte sgn = 1;
      if (c == 45) {
        sgn = -1;
        c = this.read();
      }

      int res = 0;

      while (c >= 48 && c <= 57) {
        res *= 10;
        res += c - 48;
        c = this.read();
        if (isSpaceChar(c)) {
          return res * sgn;
        }
      }

      throw new InputMismatchException();
    }

    public long nextLong() {
      int c;
      for (c = this.read(); isSpaceChar(c); c = this.read()) {
      }

      byte sgn = 1;
      if (c == 45) {
        sgn = -1;
        c = this.read();
      }

      long res = 0;

      while (c >= 48 && c <= 57) {
        res *= 10L;
        res += c - 48;
        c = this.read();
        if (isSpaceChar(c)) {
          return res * sgn;
        }
      }
      throw new InputMismatchException();
    }

    public String next() {
      int c;
      while (isSpaceChar(c = this.read())) {
      }

      StringBuilder result = new StringBuilder();
      result.appendCodePoint(c);

      while (!isSpaceChar(c = this.read())) {
        result.appendCodePoint(c);
      }

      return result.toString();
    }

    public static boolean isSpaceChar(int c) {
      return c == 32 || c == 10 || c == 13 || c == 9 || c == -1;
    }

    public long[] nextLongArray(int n) {
      long[] arr = new long[n];
      for (int i = 0; i < n; i++) {
        arr[i] = nextLong();
      }
      return arr;
    }

  }

  static class ArrayUtils {

    public static void reverse(long[] arr) {
      for (int i = 0; i < arr.length / 2; i++) {
        long temp = arr[i];
        arr[i] = arr[arr.length - i - 1];
        arr[arr.length - i - 1] = temp;
      }
    }

    public static void sort(long[] arr) {
      int n = arr.length;
      Random r = new Random();
      for (int i = 0; i < n; i++) {
        int p = r.nextInt(n + 1);
        if (p < n) {
          long temp = arr[i];
          arr[i] = arr[p];
          arr[p] = temp;
        }
      }
      Arrays.sort(arr);
    }

  }
}