HackerRank Beautiful Triplets challenge

beautifulTriplets.py

# Given a sequence of integers , a triplet  is beautiful if:

# Given an increasing sequenc of integers and the value of , count the number of beautiful triplets in the sequence.

# Example


# There are three beautiful triplets, by index: . To test the first triplet,  and .

# Function Description

# Complete the beautifulTriplets function in the editor below.

# beautifulTriplets has the following parameters:

# int d: the value to match
# int arr[n]: the sequence, sorted ascending
# Returns

# int: the number of beautiful triplets
# Input Format

# The first line contains  space-separated integers,  and , the length of the sequence and the beautiful difference.
# The second line contains  space-separated integers .

# Constraints

# Sample Input

# STDIN           Function
# -----           --------
# 7 3             arr[] size n = 7, d = 3
# 1 2 4 5 7 8 10  arr = [1, 2, 4, 5, 7, 8, 10]
# Sample Output

# 3
# Explanation

# There are many possible triplets , but our only beautiful triplets are  ,  and  by value, not index. Please see the equations below:




# Recall that a beautiful triplet satisfies the following equivalence relation:  where .

# Language
# Python 3

#!/bin/python3

import math
import os
import random
import re
import sys

#
# Complete the 'beautifulTriplets' function below.
#
# The function is expected to return an INTEGER.
# The function accepts following parameters:
#  1. INTEGER d
#  2. INTEGER_ARRAY arr
#

def beautifulTriplets(d, arr):
    # Write your code here
    triplets = 0
    for i in arr:
        if i+d in arr and i+d*2 in arr:
            triplets += 1
    return triplets

I found a way to get the triplet by checking if the sum of an element i+d and i+2*d is in the array.