# [LeetCode]#2367. Number of Arithmetic Triplets

**Environment: Python 3.8**

**Key technique: in**

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.

**Analysis:**

- Check nums[i]+diff and nums[i]+2*diff in nums

**Solution:**

`class Solution:`

def arithmeticTriplets(self, nums, diff):

ans=0

for i in range(len(nums)):

if nums[i]+diff in nums and nums[i]+diff*2 in nums:

ans+=1

return ans

**Submissions:**

Reference: