arithmetic_triplet.py

# You are given a 0-indexed, strictly increasing integer array nums and a positive integer diff. A triplet (i, j, k) is an arithmetic triplet if the following conditions are met:

# i < j < k,
# nums[j] - nums[i] == diff, and
# nums[k] - nums[j] == diff.
# Return the number of unique arithmetic triplets.

 

# Example 1:

# Input: nums = [0,1,4,6,7,10], diff = 3
# Output: 2
# Explanation:
# (1, 2, 4) is an arithmetic triplet because both 7 - 4 == 3 and 4 - 1 == 3.
# (2, 4, 5) is an arithmetic triplet because both 10 - 7 == 3 and 7 - 4 == 3. 
# Example 2:

# Input: nums = [4,5,6,7,8,9], diff = 2
# Output: 2
# Explanation:
# (0, 2, 4) is an arithmetic triplet because both 8 - 6 == 2 and 6 - 4 == 2.
# (1, 3, 5) is an arithmetic triplet because both 9 - 7 == 2 and 7 - 5 == 2.
 

# Constraints:

# 3 <= nums.length <= 200
# 0 <= nums[i] <= 200
# 1 <= diff <= 50
# nums is strictly increasing.


def arithmeticTriplets(nums, diff):
    triplets = 0
    for i in range(len(nums) - 2):
        for j in range(i + 1, len(nums) - 1):
            if nums[j] - nums[i] == diff:
                k = j + 1
                while k < len(nums):
                    if nums[k] - nums[j] == diff:
                        triplets += 1
                        break
                    k += 1
    return triplets