return_duplicates.py

def return_duplicates(arr):
    set = {}
    for x in arr:
        if x in set:
            set[x] = 2
        else:
            set[x] = 1
    
    ret = []
    for y in set.keys():
        if set[y] == 2:
            ret.append(y)
        
    return ret
    
print rem_dup([3,5,9,6,8,4,6,8,4,6,7,9,1,6,9,1])