RogerBW's Blog

The Weekly Challenge 207: Indexed Keyboards 12 March 2023

I’ve been doing the Weekly Challenges. The latest involved letter sorting and an array calculation. (Note that this closes today.)

Task 1: Keyboard Word

You are given an array of words.

Write a script to print all the words in the given array that can be types using alphabet on only one row of the keyboard.


sub keyboardword($wl) {
  return [grep /^([qwertyuiop]+|[asdfghjkl]+|[zxcvbnm]+)$/i, @{$wl}];

Languages with less-embedded regexps are a little more faff, such as JavaScript:

function keyboardword(wl) {
    let re = /^([qwertyuiop]+|[asdfghjkl]+|[zxcvbnm]+)$/i;
    let out = []
    for (let w of wl) {
        if ( > -1) {
    return out;

Lua has regex-like patterns but without alternation, so I just check each one separately.

PostScript doesn't have a pattern engine at all, so I build a dict with a row number for each letter, build another dict with all the row numbers I find, and pass on the word if there's just one row.

Task 2: H-Index

You are given an array of integers containing citations a researcher has received for each paper.

Write a script to compute the researcher’s H-Index. For more information please checkout the wikipedia page.

One of the few occasions on which a 1-based index is actually useful. Lua:

function h_index(c0)
   local c = c0
   table.sort(c, function(a, b) return b < a end)
   local h = 0
   for i, x in ipairs(c) do
      if i <= x then
         h = i
   return h

And in PostScript, made much easier by library functions:

/h_index {
    2 dict begin
    0 exch
    quicksort reverse enumerate.array {
        aload pop
        /x exch def
        1 add /i1 exch def
        i1 x le {
            pop i1
        } {
        } ifelse
    } forall
} bind def

Full code on github.

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