Count number of pairs with absolute difference k

#[test]
fn test_all_same() {
    let start = std::time::Instant::now();
    let val = Solution::count_k_difference(vec![1, 1, 1], 1);
    let expected = 0;
    log_result!(val == expected, "test_all_same", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_basic() {
    let start = std::time::Instant::now();
    let val = Solution::count_k_difference(vec![1, 2, 2, 1], 1);
    let expected = 4;
    log_result!(val == expected, "test_basic", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_no_pairs() {
    let start = std::time::Instant::now();
    let val = Solution::count_k_difference(vec![1, 3], 3);
    let expected = 0;
    log_result!(val == expected, "test_no_pairs", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_single() {
    let start = std::time::Instant::now();
    let val = Solution::count_k_difference(vec![5], 1);
    let expected = 0;
    log_result!(val == expected, "test_single", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn test_three_pairs() {
    let start = std::time::Instant::now();
    let val = Solution::count_k_difference(vec![3, 2, 1, 5, 4], 2);
    let expected = 3;
    log_result!(val == expected, "test_three_pairs", start, &expected, &val);
    assert_eq!(val, expected);
}