Number of arithmetic triplets

Array Hash Table Two Pointers Enumeration

85.4% acceptance

Feb 25, 2026

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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.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

use std::collections::HashSet;


impl Solution {
  pub fn arithmetic_triplets(nums: Vec<i32>, diff: i32) -> i32 {
    let set: HashSet<i32> = nums.iter().cloned().collect();
    nums.iter()
      .filter(|&&k| set.contains(&(k - diff)) && set.contains(&(k - 2 * diff)))
      .count() as i32
  }
}