Here is my solution but I still fail two test cases, does anyone have any recommendation to fix it, many thanks!

def countTriplets(arr, r):
dict={}
for i in arr:
    if not dict.get(i):
               dict[i]=[i*r,1]
    else:
        dict[i][1]+=1
temp=list(dict.keys())
print (temp)
print (dict)
result=0
for i in temp:
    if r==1:
        result+=dict.get(i)[1]*(dict.get(i)[1]-1)*(dict.get(i)[1]-2)/6
    elif dict.get(dict.get(i)[0])!=None and dict.get(dict.get(dict.get(i)[0])[0])!=None:
        first=i
        second=dict.get(first)[0]
        third=dict.get(second)[0]
        result+=dict.get(first)[1]*dict.get(second)[1]*dict.get(third)[1]

return int(result)