RogerBW's Blog

I’ve been doing the Weekly Challenges. The latest involved fiddling with strings. (Note that this ends today.)

Task 1: Circular

You are given a list of words.

Write a script to find out whether the last character of each word is the first character of the following word.

This is pretty straightforward in most languages, for example Raku:

sub circular(@a) {
    for @a.rotor(2 => -1) -> @p {
        if (substr(@p[0], *-1, 1) ne substr(@p[1], 0, 1)) {
            return False;
        }
    }
    True;
}

though probably the shortest is Python, where strings are half-way to character arrays already.

Task 2: Subsequence

You are given two string.

Write a script to find out if one string is a subsequence of another.

A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters.

this is quite reminiscent of #313 part 1, though slightly less fiddly. JavaScript:

function subsequence(a, b) {

Put the longer string in l and the shorter in s.

    let l = a;
    let s = b;
    if (a.length < b.length) {
        l = b;
        s = a;
    }

We're looking for the characters in s, in order.

    const st = s.split("");
    let si = 0;

Look through the characters of l.

    for (let c of l.split("")) {

If it matches the character in s we're looking for,

        if (c == st[si]) {

Increment the search counter and exit if we've found all characters.

            si += 1;
            if (si >= st.length) {
                return true;
            }
        }
    }

If that didn't happen, return fasle.

    return false;
}

Full code on github.