RogerBW's Blog

The Weekly Challenge 263: Targets Merge 07 April 2024

I’ve been doing the Weekly Challenges. The latest involved list and hash hunting. (Note that this ends today.)

Task 1: Target Index

You are given an array of integers, @ints and a target element $k.

Write a script to return the list of indices in the sorted array where the element is same as the given target element.

This is pretty close to being a one-liner in most languages. Even in PostScript it's not huge (with some of my extensions):

/targetindex {
    0 dict begin
    /k exch def
    quicksort
    enumerate.array
    { 1 get k eq } filter
    { 0 get } map
    end
} bind def

and in Rust it's quite straightforward:

fn targetindex(a0: Vec<u32>, k: u32) -> Vec<usize> {
    let mut a = a0;
    a.sort();
    a.iter()
        .enumerate()
        .filter(|(_i, v)| **v == k)
        .map(|(i, _v)| i)
        .collect::<Vec<_>>()
}

Task 2: Merge Item

You are given two 2-D array of positive integers, $items1 and $items2 where element is pair of (item_id, item_quantity).

Write a script to return the merged items.

These arrays are in effect hashes with the possibility of duplicate keys, which makes it obvious how to store the merged values. Perl:

sub mergeitems($aa, $bb) {
  my %c;
  foreach my $v ($aa, $bb) {
    foreach my $w (@{$v}) {

Add each value to its corresponding key in the output hash.

      $c{$w->[0]} += $w->[1];
    }
  }

Then rebuild the array structure based on sorted keys.

  return [map {[$_, $c{$_}]} sort {$a <=> $b} keys %c];
}

Full code on github.

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