# [LeetCode]#2367. Number of Arithmetic Triplets

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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 = 3Output: 2Explanation:(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:

1. 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:

https://leetcode.com/problems/number-of-arithmetic-triplets/discuss/2395275/Python-oror-Easy-Approach

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