Find duplicate numbers in array

#include < stdio.h > 
#include < stdlib.h > 
#define print(x) printf("%d", x);
int main() {
  int arr[] = {1,2,3,4,5,6,3,4,5,8,5,4,7,5,1,4,5,2,4,5};
  // create a auto balancing tree from given numbers for faster execution

  // we will use naive method for traversing
  // find maximum
  int max = 0;
  for (int i = 0; i < sizeof(arr) / sizeof(int); i++) {
    if ( * (arr + i) > max) max = * (arr + i);
  }

  int * arrC = malloc(max * sizeof(int));
  // make all zero
  for (int i = 0; i < max; i++) {
    *(arr + i) = 0;
  }
  // traverse tree... If more than one than do not print
  for (int i = 0; i < sizeof(arr) / sizeof(int); i++) {
    if ( * (arr + i) == 0) {
      printf("%d,", i + 1);*(arr + i) += 1;
    }
  }
  return 0;
}