A brute force solution, good to compare against a routine:

// Complete the solve function below.
static int[] solve(int[] h, int difference, int[][] queries) {
    List<int> ret = new List<int>();
    for(int query=0; query < queries.Length; query++)
    {
        int inicio = queries[query][0];
        int fim = queries[query][1];
        int total = 0;
        for(int iextertno = inicio; iextertno < fim; iextertno++)
        {
            for(int iinterno = iextertno+1; iinterno <= fim; iinterno++)
            {
                int diff = Math.Abs(h[iextertno] - h[iinterno]);
                if(diff <= difference)
                    total++;
            }
        }
        ret.Add(total);
    }
    return ret.ToArray();
}