Daily Challenge #266 - Who Likes It?

#challenge

dev.to staff Jul 8, 2020 ・1 min read

You probably know the "like" system from Facebook and other pages. People can "like" blog posts, pictures or other items. We want to create the text that should be displayed next to such an item.

Implement a function likes :: [String] -> String, which must take in input array, containing the names of people who like an item. It must return the display text as shown in these examples:

likes {} // must be "no one likes this"
likes {"Peter"} // must be "Peter likes this"
likes {"Jacob", "Alex"} // must be "Jacob and Alex like this"
likes {"Max", "John", "Mark"} // must be "Max, John and Mark like this"
likes {"Alex", "Jacob", "Mark", "Max"} // must be "Alex, Jacob and 2 others like this"

For 4 or more names, the number in and 2 others simply increases.

Good luck!

This challenge comes from BattleRattle on CodeWars. Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!

Want to propose a challenge idea for a future post? Email yo+challenge@dev.to with your suggestions!

Discussion (27)

willsmart • Jul 8 '20

This'd be a good use for template literals. Here's a quicky in javascript:

function likesStringForNames(names) {
  const [first, second, third] = names;
  switch (names.length) {
    case 0: return "no one likes this";
    case 1: return `${first} likes this`;
    case 2: return `${first} and ${second} like this`;
    case 3: return `${first}, ${second} and ${third} like this`;
    default: return `${first}, ${second} and ${names.length - 2} others like this`;
  }
}

Sanity check:

[
  [],
  ["Peter"],
  ["Jacob", "Alex"],
  ["Max", "John", "Mark"],
  ["Alex", "Jacob", "Mark", "Max"],
  ["Alex", "Mark", ...Array(10000)]
].map(likesStringForNames)
-->
[
  "no one likes this",
  "Peter likes this",
  "Jacob and Alex like this",
  "Max, John and Mark like this",
  "Alex, Jacob and 2 others like this",
  "Alex, Mark and 10000 others like this"
]

peter279k • Jul 9 '20

Here is the code snippets with PHP:

function likes( $names ) {
    $namesCount = count($names);
    if ($namesCount === 0) {
        return "no one likes this";
    }

    if ($namesCount === 1) {
        return sprintf("%s likes this", $names[0]);
    }

    if ($namesCount === 2) {
        return sprintf("%s and %s like this", $names[0], $names[1]);
    }

    if ($namesCount === 3) {
        return sprintf("%s, %s and %s like this", $names[0], $names[1], $names[2]);
    }

    if ($namesCount >= 4) {
        $likesStringFormat = "%s, %s and %d others like this";

        $otherNamesCount = $namesCount - 2;

        return sprintf($likesStringFormat, $names[0], $names[1], $otherNamesCount);
    }
}

Edison Pebojot(👨‍💻) • Jul 8 '20 • Edited

For cleverness, we can solve it like this in JavaScript:

Bonus

For best practice and cleverness, we can do this in JavaScript:

And for the most best practice and cleverness, we can do this in JavaScript:

JP Antunes • Jul 8 '20 • Edited

I think you don't need the break after the return, it would be unreachable.

const likes = (arr = []) => {
    switch (arr.length) {
        case 0:
            return "no one likes this";
        case 1:
            return `${arr[0]} likes this`;
        case 2:
            return `${arr[0]} and ${arr[1]} like this`;
        case 3:
            return `${arr[0]}, ${arr[1]} and ${arr[2]} like this`;
        default:
            return `${arr[0]}, ${arr[1]} and ${arr.length - 2} others like this`;
    }
}

Edison Pebojot(👨‍💻) • Jul 9 '20 • Edited

Thank you for pointing out that! 👍👍

Functional Javascript • Jul 9 '20

This is a case where the switch block is probably the simplest idiom with the least cognitive load.

Having to use Math.min, conditional Regex's, replace callbacks, and array shifts, would be unnecessary complexity.

Good work showing the variants to outline the pros and cons though.

Functional Javascript • Jul 9 '20

The exception would be if the more "complex" solution was more performant.

For verification, I ran a perf test on the two funcs, and the switch idiom won out. (see screenshot below).

If another idiom were to beat out the switch idiom, I would swap out the implementation for the fastest idiom that uses the least cycles.
Wrap it in a function, document it, and include a resource link to the performance notes, tests and reasoning of the chosen implementation.

Jericho Reyes • Jul 8 '20

The last part is, in my opinion , the best part I've ever seen

Hayden Mankin • Jul 8 '20

let likes = ([a, b, ...c]) => c.length > 1 ? `${a}, ${b} and ${c.length} others like this` : c.length ? `${a}, ${b} and ${c[0]} like this` : b ? `${a} and ${b} like this` : a ? `${a} likes this` : `no one likes this`;

console.log(likes([])); // no one likes this
console.log(likes(["Peter"])); // Peter likes this
console.log(likes(["Jacob", "Alex"])); // Jacob and Alex like this
console.log(likes(["Max", "John", "Mark"])); // Max, John and Mark like this
console.log(likes(["Alex", "Jacob", "Mark", "Max"])); // Alex, Jacob and 2 others like this

Valts Liepiņš • Jul 9 '20

Very declarative Haskell solution:

likes :: [String] -> String
likes []     = "no one likes this"
likes [name] = name <> " likes this"
likes names  = showMultiple names <> " like this"

showMultiple :: [String] -> String
showMultiple xs = case xs of
  []          -> ""
  [x]         -> x
  [x,x']      -> x <> " and " <> x'
  [x,x',x'']  -> x <> ", " <> showMultiple [x',x'']
  (x:x':rest) -> x <> ", " <> x' <> " and " <> (show $ length rest) <> " others"

Mofid Jobakji • Jul 9 '20

 const likes = (names) => {
   const map = new Map([
     [0, 'no one likes this'],
     [1, '{name} likes this'],
     [2, '{name} and {name} like this'],
     [3, '{name}, {name} and {name} like this'],
     [4, '{name}, {name} and {n} others like this'],
   ]);

   return map
   .get(names.length < 4 ? names.length : 4)
     .replace(/{name}|{n}/g, (val) =>
       val === '{name}' ? names.shift() : names.length
     );
 };

Manolo Edge • Jul 9 '20

Cool I did this one 3 years ago over at CodeWars, here is the answer I posted:

function likes(names) {
  switch(names.length){
    case 0:  return `no one likes this`; break;
    case 1:  return `${names[0]} likes this`; break;
    case 2:  return `${names[0]} and ${names[1]} like this`; break;
    case 3:  return `${names[0]}, ${names[1]} and ${names[2]} like this`; break;
    default: return `${names[0]}, ${names[1]} and ${names.length - 2} others like this`;
  }
}

Manolo Edge • Jul 9 '20

Looking at it now,break is not needed, as return breaks out of the switch statement.

Ilyes Chouia • Aug 14 '20 • Edited

The solution in PHP

function likes(array $names): string
{
  $likeWord = "like";
  $string = "";
  switch(count($names)){
    case 0:
      $string = sprintf("No one %s this", $likeWord."s");
      break;
    case 1:
      $string = sprintf("%s %s this", $names[0],$likeWord."s");
      break;
    case 2:
      $string = sprintf("%s and %s %s this", $names[0], $names[1], $likeWord);
      break;
    case 3:
      $string = sprintf("%s, %s and %s %s this", $names[0], $names[1], $names[2], $likeWord);
      break;
    default:
      $string = sprintf("%s, %s and %s others %s this", $names[0], $names[1], count($names) - 2 , $likeWord);
  }
  return $string;
}

SavagePixie • Jul 8 '20

Elixir

There's probably a much simpler way to solve it, but hey, I basically know how to do pattern matching and recursion, so there we go:

defmodule Like do
  def who_likes(list) do
    count = Enum.count(list)
    _who_likes(list, count - 2)
    |> _add_likes(count)
    |> IO.puts
  end

  defp _add_likes(x, n) when (n < 2), do: "#{x} likes this"
  defp _add_likes(x, _), do: "#{x} like this"

  defp _who_likes([], _), do: "no one"
  defp _who_likes([ a | [] ], _), do: a
  defp _who_likes([ a, b | [] ], _), do: "#{a} and #{b}"
  defp _who_likes([ a, b, c | [] ], _), do: "#{a}, #{b} and #{c}"
  defp _who_likes([ a, b | _tail], count), do: "#{a}, #{b} and #{count} others"
end

Amin • Jul 8 '20 • Edited

TypeScript

const likes = ([a, b, c, ...xs]: string[]): string =>
    a === undefined
        ? "No one likes this."
        : b === undefined
            ? `${a} likes this.`
            :  c === undefined
                ? `${a} and ${b} like this.`
                : xs.length === 0
                    ? `${a}, ${b} and ${c} like this.`
                    : `${a}, ${b} and ${[c, ...xs].length} others like this.`;

Sam Ferree • Jul 8 '20

C# switch expressions to the rescue!

public static class Format
{
  public static string LikeText(string[] names) => names.Length switch
  {
    0 => "no one likes this",
    1 => $"{names[0]} likes this",
    2 => $"{names[0]} and {names[1}} like this",
    3 => $"{names[0]}, {names[1]}, and {names[2]} like this",
    _ => $"{names[0]}, {names[1]}, and {names.Length-2} others  like this",
  };
}

Mark • Jul 8 '20 • Edited

This is what I got with Ruby, not a lover of it though - any Ruby devs got some alternatives?

def like_text(names = [])
  count = names.count

  string = case count
           when 0
            "no one likes this"
           when 1
            "#{names.first} likes this"
           when 2
            "#{names.join(' and ')} like this"
           when 3
            "#{names.first(2).join(', ')} and #{names.last} like this"
           else
            "#{names.first(2).join(', ')} and #{names.count - 2} others like this"
           end
end

With Rails, I'm fairly certain two of these can be solved with to_sentence 🙌

Dimitri Lahaye • Jul 8 '20

Here is my proposition in JS:

function whoLike(names) {
  const l = names.length;
  if (!l) {
    return 'No one likes this';
  } else if (l === 1) {
    return `${names[0]} likes this.`;
  } else if (l < 4) {
    return `${names.slice(0, l - 1).join(', ')} and ${names[l - 1]} like this.`;
  }
  return  `${names.slice(0, 2).join(', ')} and ${l - 2} others like this.`;
}

#benaryorg • Jul 8 '20

Strings in Rust are a bit tedious since you usually want to avoid extra allocations and there's ownership concerns, so this code has a lot more refs than I'd like, and the function signature is a classic, but otherwise I think it's kind of pretty.
What I like most is that there's no -2 for the length, because Rust pattern matching lets me capture the elements into another slice right there.

fn like_text<S: AsRef<str>>(likes: &[S]) -> String
{
    match likes
    {
        &[] => "no one likes this".to_string(),
        &[ref one] => format!("{} likes this", one.as_ref()),
        &[ref one, ref two] => format!("{} and {} like this", one.as_ref(), two.as_ref()),
        &[ref one, ref two, ref three] => format!("{}, {} and {} like this", one.as_ref(), two.as_ref(), three.as_ref()),
        &[ref one, ref two, ref rest@..] => format!("{}, {} and {} others like this", one.as_ref(), two.as_ref(), rest.len())
    }
}

fn main()
{
    let likes = ["foo", "bar", "baz", "quux"];

    println!("{}", like_text(&likes))
}

Permalink to the Rust Playground: play.rust-lang.org/?version=stable...

MxL Devs • Jul 8 '20 • Edited

Ruby string-formatting takes an array of arguments, so if my function takes an array of names, then I just need to feed it into some pre-formatted "templates". Also the use of splat-array which I don't completely understand actually.

def likes(names)
  num_people = names.size
  case num_people
  when 0
    "no one likes this"
  when 1
    "%s likes this" %names
  when 2
    "%s and %s like this" %names
  when 3
    "%s, %s and %s like this" %names
  else
    "%s, %s and %d others like this" %[*names[0..1], num_people - 2] 
  end
end

p likes [] # must be "no one likes this"
p likes ["Peter"] # must be "Peter likes this"
p likes ["Jacob", "Alex"] # must be "Jacob and Alex like this"
p likes ["Max", "John", "Mark"] # must be "Max, John and Mark like this"
p likes ["Alex", "Jacob", "Mark", "Max"] # must be "Alex, Jacob and 2 others like this"

Andrea Stagi • Jul 8 '20 • Edited

For Python


def who_likes_this(names: list) -> str:
    who = 'no one'
    number_of_likes = len(names)
    if number_of_likes > 0 and number_of_likes < 3 :
        who = ' and '.join(names)
    elif number_of_likes >= 3:
        who = ', '.join(names[:2])
        who += ' and ' + (names[2] if number_of_likes == 3 else f' and {len(names[2:])} others')
    return f'{who} like{"" if number_of_likes > 1 else "s" } this'

Test it:

print (who_likes_this([]))
print (who_likes_this(["Peter"]))
print (who_likes_this(["Jacob", "Alex"]))
print (who_likes_this(["Max", "John", "Mark"]))
print (who_likes_this(["Alex", "Jacob", "Mark", "Max"]))
print (who_likes_this(["Alex", "Jacob", "Mark", "Max", "Peter"]))

Rafael Acioly • Jul 9 '20 • Edited

Here's my version :)

from typing import List


def likes(names: List[str]) -> str:
  messages = {
    0: 'no one likes this',
    1: '%s likes this',
    2: '%s and %s like this',
    3: '%s, %s and %s like this'
  }

  message = messages.get(len(names))
  if not message:
    return '%s, %s and %d others like this' % (*names[:2], len(names) - 2)

  return message % tuple(names)

David Jensen • Jul 9 '20 • Edited

Javascript one-liner.
The cutoff can be changed.

let summarizeNamesAtNumNames = 4;
const likes = (names) =>
  [
    names.length === 0
      ? "no one"
      : names
          .slice(0, summarizeNamesAtNumNames - 1)
          .reduce(
            (acc, name, index) =>
              acc +
              (index === 0
                ? ""
                : index ===
                  Math.min(names.length - 1, summarizeNamesAtNumNames - 2)
                ? " and "
                : ", ") +
              (names.length >= summarizeNamesAtNumNames &&
              index === summarizeNamesAtNumNames - 2
                ? names.length - (summarizeNamesAtNumNames - 2) + " others"
                : name),
            ""
          ),
    "like" + (names.length <= 1 ? "s" : ""),
    "this",
  ].join(" ");

for (let cut = 2; cut < 7; cut++) {
  summarizeNamesAtNumNames = cut;
  console.log(likes([]));
  console.log(likes(["Peter"]));
  console.log(likes(["Jacob", "Alex"]));
  console.log(likes(["Max", "John", "Mark"]));
  console.log(likes(["Alex", "Jacob", "Mark", "Max"]));
  console.log(likes(["Alex", "Jacob", "Mark", "Max", "Joey", "Joe Joe"]));
  console.log(
    likes(["Alex", "Jacob", "Mark", "Max", "Joey", "Joe Joe", "Shabadoo"])
  );
}