2367. Number of Arithmetic Triplets

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.

class Solution {
public:
    int arithmeticTriplets(vector<int>& A, int diff) {
        int n = A.size(), res = 0;
        for(int i = 0; i < n; i++) {
            for(int j = i + 1; j < n; j++) {
                for(int k = j + 1; k < n; k++) {
                    if(A[j] - A[i] == diff and A[k] - A[j] == diff) res++;
                }
            }
        }
        return res;
    }
};