#include "mergeSort.h"

void merge(int array[], int left, int middle, int right) {
  // Keine verschachtelten Schleifen, jedoch wird jedes Element einmal
  // bearbeitet -> O(n)
  int n1 = middle - left + 1;
  int n2 = right - middle;

  int leftArray[n1];
  int rightArray[n1];

  for (int i = 0; i < n1; i++) {
    leftArray[i] = array[left + i];
  }
  for (int j = 0; j < n2; j++) {
    rightArray[j] = array[middle + j + 1];
  }

  int k = 0, l = 0, m = left;
  while (k < n1 && l < n2) {
    if (leftArray[k] <= rightArray[l]) {
      array[m] = leftArray[k];
      k++;
    } else {
      array[m] = rightArray[l];
      l++;
    }
    m++;
  }

  while (k < n1) {
    array[m] = leftArray[k];
    k++;
    m++;
  }

  while (l < n2) {
    array[m] = rightArray[l];
    l++;
    m++;
  }
}

void mergeSort(int array[], int left, int right) {
  if (left < right) {
    int middle = left + (right - left) / 2;

    // O(T(n/2))
    mergeSort(array, left, middle);
    // O(T(n/2))
    mergeSort(array, middle + 1, right);
    // O(n)
    merge(array, left, middle, right);
  }
}
//
// Insgesamt: 2 * O(T(n/2)) + O(n) -> Master Theorem -> O(n log n)