package cse1030;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class ArrayMath {
  public static double[] cos(double[] a) {
    double[] result = new double[a.length];
    for (int i = 0; i < a.length; i++) {
      result[i] = Math.cos(a[i]);
    }
    return result;
  }
  
  public static double[] sin(double[] a) {
    double[] result = new double[a.length];
    for (int i = 0; i < a.length; i++) {
      result[i] = Math.sin(a[i]);
    }
    return result;
  }
  
  public static double[] tan(double[] a) {
    double[] result = new double[a.length];
    for (int i = 0; i < a.length; i++) {
      result[i] = Math.tan(a[i]);
    }
    return result;
  }
  
  public static double max(double[] a) {
    double currentMax = Double.NEGATIVE_INFINITY;
    for (int i = 0; i < a.length; i++) {
      if (a[i] > currentMax) {
        currentMax = a[i];
      }
    }
    return currentMax;
  }
  
  public static double min(double[] a) {
    double currentMin = Double.POSITIVE_INFINITY;
    for (int i = 0; i < a.length; i++) {
      if (a[i] < currentMin) {
        currentMin = a[i];
      }
    }
    return currentMin;
  }
  
  public static double mean(double[] a) {
    double mu = 0.0;
    for (int i = 0; i < a.length; i++) {
      mu += a[i] / a.length;
    }
    return mu;
  }
  
  public static int[] mode(int[] a) {
    // count the number of times each element appears in a
    Map<Integer, Integer> m = new HashMap<Integer, Integer>();
    for (Integer key : a) {
      Integer count = m.get(key);
      if (count == null) {
        m.put(key, 1);
      }
      else {
        m.put(key,  count + 1);
      }
    }
    // find the largest value in the map;
    // the corresponding key is a mode (there may be multiple modes)
    Integer modeCount = Collections.max(m.values());
    // find all of the modes
    List<Integer> modes = new ArrayList<Integer>();
    for (Map.Entry<Integer, Integer> entry : m.entrySet()) {
      if (entry.getValue().equals(modeCount)) {
        modes.add(entry.getKey());
      }
    }
    // copy the modes into an array of int
    int[] result = new int[modes.size()];
    for (int i = 0; i < modes.size(); i++) {
      result[i] = modes.get(i);
    }
    return result;
  }
}