Program(python):-Find duplicates in an array (Geeks for geek problem)

QUESTION:-

Given an array a of size N which contains elements from 0 to N-1, you need to find all the elements occurring more than once in the given array. Return the answer in ascending order. If no such element is found, return list containing [-1]. 

Note: The extra space is only for the array to be returned. Try and perform all operations within the provided array. 

Example 1:

Input:
N = 4
a[] = {0,3,1,2}
Output: 
-1
Explanation: 
There is no repeating element in the array. Therefore output is -1.

Example 2:

Input:
N = 5
a[] = {2,3,1,2,3}
Output: 
2 3 
Explanation: 
2 and 3 occur more than once in the given array.

Your Task:
Complete the function duplicates() which takes array a[] and n as input as parameters and returns a list of elements that occur more than once in the given array in a sorted manner. 

Expected Time Complexity: O(n).
Expected Auxiliary Space: O(n).

Constraints:
1 <= N <= 105
0 <= A[i] <= N-1, for each valid i

SOLUTION:-

class Solution:

    def duplicates(self, arr, n): 

        l=list()

        d={}

        for c in arr:

            d.setdefault(c,0)

            d[c]=d[c]+1

        for k,v in d.items():

            if(v>1):

                l.append(k)

        if len(l)==0:

            l=[-1]

        else:

            l.sort()

        return l

                

    # code here

        

#{ 

 # Driver Code Starts

if(__name__=='__main__'):

    t = int(input())

    for i in range(t):

        n = int(input())

        arr = list(map(int, input().strip().split()))

        res = Solution().duplicates(arr, n)

        for i in res:

            print(i,end=" ")

        print()

# } Driver Code Ends