package algs11;
import stdlib.*;
import java.util.Arrays;
public class XArrayFunctions {

  public static double average (double[] a) {
    int N = a.length;
    double sum = 0.0;
    for (int i = 0; i < N; i++)
      sum += a[i];
    double average = sum / N;
    return average;
  }

  public static double[] copy (double[] a) {
    int N = a.length;
    double[] b = new double[N];
    for (int i = 0; i < N; i++)
      b[i] = a[i];
    return b;
  }

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

  public static double[][] multiply (double[][] a, double[][] b) {
    int N = a.length;
    double[][] c = new double[N][N];
    for (int i = 0; i < N; i++)
      for (int j = 0; j < N; j++)
        // Compute dot product of row i and column j.
        for (int k = 0; k < N; k++)
          c[i][j] += a[i][k] * b[k][j];
    return c;
  }

  public static void main (String[] args) {
    double[] a = new double[] { 10, 20, 30, 40, 50 };

    StdOut.format ("average: %f\n", average (a));

    double[] b = copy (a);
    reverse (b);
    StdOut.format ("reverse: %s\n", Arrays.toString (b));
  }
}