void printRepeating(int arr[], int size)
{
  int *count = (int *)calloc(sizeof(int), (size - 2));
  int i;

  printf(" Repeating elements are ");
  for(i = 0; i < size; i++)
  {
    if(count[arr[i]] == 1)
      printf(" %d ", arr[i]);
    else
     count[arr[i]]++;
  }
}

a=[1,2,3,2,4,3,1,7,4,3];
b=[];
for i in a:
        b[i]=b[i]+1;

IndexError: list index out of range

a = [1,2,3,2,4,3,1,7,4,3]
b = {}
for i in a:
    # get(key, default) falls back to default if key is not present
    b[i] = b.get(i, 0) + 1

> b
{1: 2, 2: 2, 3: 3, 4: 2, 7: 1}
> b[3]
3

a = [1,2,3,2,4,3,1,7,4,3]
print("Repeating elements are")
for i in a:
    if a.count(i) > 1:
        print(i)

from collections import Counter
a = [1,2,3,2,4,3,1,7,4,3]
counter = Counter(a)
print(a.most_common())

a=[1,2,3,2,4,3,1,7,4,3]
b={}
for i in a:
    if i in b:
        b[i]+=1
    else:
        b[i]=1