Count common words with one occurrence

#[test]
fn t1() {
    let start = std::time::Instant::now();
    let val = Solution::count_words(
            sv(&["leetcode", "is", "amazing", "as", "is"]),
            sv(&["amazing", "leetcode", "is"])
        );
    let expected = 2;
    log_result!(val == expected, "t1", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t2() {
    let start = std::time::Instant::now();
    let val = Solution::count_words(sv(&["b", "bb", "bbb"]), sv(&["a", "aa", "aaa"]));
    let expected = 0;
    log_result!(val == expected, "t2", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t3() {
    let start = std::time::Instant::now();
    let val = Solution::count_words(sv(&["a", "ab"]), sv(&["a", "a", "a", "ab"]));
    let expected = 1;
    log_result!(val == expected, "t3", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t4() {
    let start = std::time::Instant::now();
    // Both have one occurrence of "hello"
    let val = Solution::count_words(sv(&["hello", "world"]), sv(&["hello", "rust"]));
    let expected = 1;
    log_result!(val == expected, "t4", start, &expected, &val);
    assert_eq!(val, expected);
}

#[test]
fn t5() {
    let start = std::time::Instant::now();
    // Duplicate in both arrays - not counted
    let val = Solution::count_words(sv(&["x", "x", "y"]), sv(&["x", "y", "y"]));
    let expected = 0;
    log_result!(val == expected, "t5", start, &expected, &val);
    assert_eq!(val, expected);
}