[HackerRank] Beautiful Triplets

[コード]

def beautifulTriplets(d, arr):
    # Write your code here
    result = 0
    for idx in range(1 , len(arr)-1):
        upper = arr[idx+1:].count(arr[idx]+d)
        lower = arr[0:idx].count(arr[idx]-d)
        
        result += (upper*lower)
    return result