Number of Arithmetic Triplets — LeetCode 2367 Python Solution

The problem

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.

Example

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.

Python solution

class Solution:
    def arithmeticTriplets(self, nums: List[int], diff: int) -> int:
        return sum(b - a == diff and c - b == diff for a, b, c in combinations(nums, 3))

Complexity

Pattern: Two Pointers

Use the order already in the input to discard half the search space at every step. LeetCode 2367. Number of Arithmetic Triplets is filed here because LeetCode tags it Two Pointers, which is the vocabulary this hub collects.

The two pointers guide has the Python template for the pattern and the 201 LeetCode problems that use it.

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