Merge sort ansi C

#include <stdio.h>
#include <stdlib.h>

#define LEN 10
void merge(int *V, size_t left, size_t mid, size_t right);
void merge_sort(int *V, size_t i, size_t j);
void print_arr(int *V, size_t length);

int main(void) {
  int arr[LEN] = {
    4, 6, 10, 10, 1, 9, 11, 15, -1, 1
  };

  printf("Unsorted:\n");
  print_arr(arr, LEN);
  merge_sort(arr, 0, LEN - 1);

  printf("\nSorted:\n");
  print_arr(arr, LEN);
  return 0;
}

void print_arr(int *V, size_t length) {
  printf("[ ");
  for (size_t i = 0; i < length; i++)
    printf("%d ", V[i]);
  printf("]");
}

void merge(int *V, size_t left, size_t mid, size_t right) {
  int *T = (int *)malloc(sizeof(int) * (right - left + 1));
  size_t i = left;
  size_t j = mid + 1;
  size_t t_index = 0;

  // Finchè non ho finito almeno una delle 2 fusioni
  // T(n) = O(n)
  while (i <= mid && j <= right) {
    if (V[i] < V[j]) {
      T[t_index++] = V[i++];
    } else {
      T[t_index++] = V[j++];
    }
  }

  // Ciò che rimane del left
  // T(n) = O(n)
  while (i <= mid) {
    T[t_index++] = V[i++];
  }

  // Ciò che rimane del right
  // T(n) = O(n)
  while (j <= right) {
    T[t_index++] = V[j++];
  }

  // Copiamo su V
  for (size_t copy_i = left; copy_i <= right; copy_i++) {
    V[copy_i] = T[copy_i - left];
  }
}

// T(N) = 2T(n/2) + O(n)
// 2nd MT = n^logb(a)*log2n
void merge_sort(int *V, size_t i, size_t j) {
  if (i >= j)
    return;

  size_t mid = i + (j - i) / 2;
  // O(T(n / 2))
  merge_sort(V, i, mid);

  // O(T(n / 2))
  merge_sort(V, mid + 1, j);

  // O(n)
  merge(V, i, mid, j);
}