Daily Challenge #1 - String Peeler

Hey, everyone. We've decided to host a daily challenge series. We'll have a variety of challenges, ranging in difficulty and complexity. If you choose to accept the task, your goal is to write the most efficient function you can for your language. Bonus points for any features you add!

I’ll start you off with a simple, straightforward challenge. Our first one comes from user @SteadyX on CodeWars.

Your goal is to create a function that removes the first and last letters of a string. Strings with two characters or less are considered invalid. You can choose to have your function return null or simply ignore.

The fundamentals are important, it only gets more difficult from here.

Happy coding!

---

Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!

Want to propose a challenge for a future post? Email [e-mail] with your suggestions!

Comments

[Alvaro Montoro]

CSS

Just add the class removeFirstAndLastLetter to a tag, and see the first and last letter "removed" from the text 😋

.removeFirstAndLastLetter {
  background: #fff;
  font-family: monospace;
  white-space: nowrap;
  position: relative;
  display: inline-block;
}

.removeFirstAndLastLetter::before,
.removeFirstAndLastLetter::after {
  content: "\00a0";
  background: #fff;
  top: 0;
  display: block;
  position: absolute;
  height: 100%;
  width: auto;
}

.removeFirstAndLastLetter::after {
  right: 0;
}

And as an extra, it can be stylized and animated, so you can see the letters fade out:

[Ben Halpern]

Ha! This one is great.

[Alvaro Montoro]

Thanks :)

[Ryland G]

JavaScript

(someString) => someString.length > 2 ? someString.slice(1, -1) : undefined;

Python

someString[1:-1] if len(someString) > 2 else None

C++

someString.size() > 2 ? someString.substr(1, someString.size() - 1) : null;

C

int trimString(char someString[])
{
  if (strlen(someString) > 2) {
    char *copy = malloc((strlen(someString) - 2) * sizeof(char));
    memmove (copy, someString + 1, strlen(someString) - 2);
    printf("%s", copy);
    free(copy);
    return 0;
  }
  return 1;
}

[Rafael Acioly]

Let people do something 😂

[Jerome De Leon]

HAHAHA damn. Let me finish my code LOL.

[Clay Murray]

Let's just go wild

(someString) => {
   switch(someString.length){
   case 0:
   case 1:
   case 2:
       return null;
   default:
       const arr = someString.split("")
       arr.pop();
       arr.reverse();
       arr.pop();
       arr.reverse();
       return arr.join("")
   }
}

Why not?

[Ibrahim Abdullahi Aliyu]

This is indeed wild

[Alvaro Montoro]

In JavaScript it could be 24 bytes:

f=s=>s.slice(1,-1)||null

[Andrew Brown 🇨🇦]

I am surprised no one wrote test code. Sometimes in interviews with challenge this simple and you have access to run ruby they are expecting to see test code. Check out my ruby test code tutorials buds.

I notice lots of people are raising an error instead of ignoring or returning null so they have failed the challenge's instructions.

require "test/unit"

# remove the first and last letter of a string
# if there is less than 2 characters return zero.
def quartered value
  raise ArgumentError, 'Argument is not a string' unless value.is_a? String
  return value unless value.size > 2
  value[0] = ''
  value.chop
end


class QaurteredTest < Test::Unit::TestCase
  def test_quartered
    assert_equal 'orl', quartered('world'), "quartered('world') should return a string called 'orl'"
  end

  def test_quartered_ignore
    assert_equal 'hi', quartered('hi'), "quartered('hi') should return 'hi'"
  end

  def test_quartered_invalid
    assert_raise_message('Argument is not a string', "quartered(2) should raise exception") do
      quartered(2)
    end
  end
end

[Ben Halpern]

Ruby

def remove_first_and_last(string)
  raise "Invalid" if string.size < 3
  string[1..string.size-2]
end

[MetaDave 🇪🇺]

I think you can get away with string[1..-2] there, Ben.

[Ceban Dumitru]

BASH

if [[ ${#1} > 2 ]]; then
    echo "${1:1:$(($#1-2))}";
else echo "not validated";
fi

[orenovadia]

I was surprised to find that -1 to work as well:

V=abcde
echo "${V:1:-1}"

[Exequiel Beker]

I tried to not use any str function.

char* trimFirstAndLastLetters(char* str)
{
    int index = 1;

    if(str[0] == '\0' || str[1] == '\0') {
        return NULL;
    }

    while(*(str + index) != '\0') {
        *(str + (index - 1)) = *(str + index);
        index++;
    }

    /* Remove last one */
    *(str + (index - 2)) = '\0';
    return str;
}

[Corey Alexander]

Rust

fn remove_first_and_last(string: &str) -> &str {
    remove_first_and_last_n_chars(&string, 1)
}

fn remove_first_and_last_n_chars(string: &str, chars_to_remove: usize) -> &str {
    if string.len() <= (2 * chars_to_remove) {
        panic!("Input string too short")
    }
    let start = chars_to_remove;
    let end = string.len() - 1 - chars_to_remove;

    &string[start..end]
} 

fn main() {
    println!("Ans: {}", remove_first_and_last("Hello, world!"));
    println!("Ans: {}", remove_first_and_last_n_chars("Hello, world!", 2));
    println!("Ans: {}", remove_first_and_last_n_chars("aa", 1));
    println!("Ans: {}", remove_first_and_last_n_chars("aa", 2));
}

View it in the Rust Playground here: play.rust-lang.org/?version=stable...

[Bárbara Perdigão]

I wanted to take my chances with these challenges, but I decided to start from the beginning, so here's my (super) late entry, done in Java :

public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.println("Type the word:");
        String word = scan.nextLine();

        if (word.length() > 2) {
            System.out.printf("Result: %s%n", word.substring(1, word.length() - 1));
        } else {
            System.out.println("Invalid word.");
        }

}

[Andreas Jakof]

in C# as Extension-Method

public static string Peel(this string toPeel)
{
    int residual = toPeel.Length -2;
    if (residual < 1) return null;

    return toPeel.SubString(1,residual); //skip the first and take all but the last char
}

[Vladislav Guleaev]

function removeChar(str){
 return str.substr(1, str.length - 2)
};

[Martin Himmel]

PHP

function remove_string_ends($str) {
    if (strlen($str) <= 2) {
        return null;
    }
    return substr($str, 1, -1);
}

[Claudio Scatoli]

I like that substr trick with the -1, didn't think of that!

How about this one liner?

<?php

function trimThis(string $str)
{
    return (mb_strlen($str) <= 2) ? null : substr($str,1,-1);
}

---

Use mb_string to support multibyte chars, such as Chinese

Also typehinted the argument, you never know...

---

This one is even shorter, possible only if the arg is typehinted tho

<?php
function trimThis(string $str) {
    return substr($str,1,-1) ?: null;
}

When the string is shorter than 2, substr returns false;
when the length is 2, substr returns "".

In both cases it's false, the the return is null.

---

Edit: many typos, I'm on mobile :/

[Corey Alexander]

Ruby

Basic

def remove_first_and_last(some_string)
  raise 'Not long enough' unless some_string.length > 2

  some_string[1..-2]
end

Extra

def remove_first_and_last_n_characters(some_string, chars_to_remove: 1)
  raise 'Not long enough' unless some_string.length > (chars_to_remove * 2)

  start_index = chars_to_remove
  end_index = -1 - chars_to_remove
  some_string[start_index..end_index]
end

[Kasper Meyer]

Ruby solution

require "minitest/autorun"

class WordTrimmer
  def initialize word
    @word = word
  end

  def trim
    @word.length <= 2 ? @word : @word[1..-2]
  end
end

class WordTrimmerTest < MiniTest::Test
  def test_removing_first_and_last_letter
    assert_equal "aspe", WordTrimmer.new("kasper").trim
  end

  def test_ignoring_two_letter_word
    assert_equal "hi", WordTrimmer.new("hi").trim
  end

  def test_ignoring_one_letter_word
    assert_equal "I", WordTrimmer.new("I").trim
  end
end

[Tom Ekander]

ReasonML

let strip = text =>
  String.(
    length(text) > 2
      ? switch (sub(text, 1, length(text) - 2)) {
        | s => Some(s)
        | exception _ => None
        }
      : None
  );

strip("hello"); // Some("ell")
strip("ab"); // None
strip(""); // None

[jmc]

Clojure:

(defn trim [s]
  (apply str (drop-last (rest s))))

[Michael Lang]

Ruby Language Version

With specs

def trim value
  value.to_s[1...-1]
end

require "spec"

describe "#trim" do
  it { expect(trim "Foo Bar").to eq "oo Ba"}
  it { expect(trim "Foo").to eq "o"}
  it { expect(trim "Fo").to eq ""}
  it { expect(trim "F").to eq ""}
  it { expect(trim nil).to be_nil}
  it { expect(trim 777).to eq "7"}
end

output

>> rspec debook_ends.rb
......

Finished in 0.00696 seconds (files took 0.15187 seconds to load)
6 examples, 0 failures

[Rafi]

solution in SQL (postgres)

\set str 'hello world'

select (
     case
       when (select length(:'str') > 2) 
        then (select substr(:'str', 2, length(:'str') - 2) ) 
else 'invalid string' end );

[Praneet Nadkar]

In C#, I would use in built string function Trim()
In my opinion we don't need Substring() here.
Just call :

readedInput.Trim(readedInput[0], readedInput[readedInput.Length - 1])

With 2 length validation:

var trimmed = readedInput.Length > 2 ? readedInput.Trim(readedInput[0], readedInput[readedInput.Length - 1]) : "Invalid" ;

[Andreas Jakof]

But what if the input would be "aaajldflbbb"?

When using Trim(char[]), all appearances of the characters given to the method at the beginning and at the end, will be removed, leaving "jldfl".

Removes all leading and trailing occurrences of a set of characters specified in an array from the current String object.

[Aaron Stroud]

I see a lot of solutions removing characters without checking to see if they're "letters." Here's my JavaScript solution.

// Remove the first and last _letters_ in a string
function removeFirstLastLetters(str) {
  if (str.length < 3) {
    return null;
  }
  else {
    const regex = /[a-zA-Z]/;

    let firstCharIndex = str.search(regex);

    if (firstCharIndex === -1 ) {
      return null;
    }

    else {
      let lastCharIndex = str.length - str.split("").reverse().join("").search(regex);

      return str.slice(0, firstCharIndex) + str.slice(firstCharIndex + 1, lastCharIndex - 1) + str.slice(lastCharIndex, str.length);
    }
  }
}

[George Offley]

Off the top of the head in Python 🐍🐍🐍🐍

def strip_first_last(string):
     if len(string) > 2:
          return string[1:-1]
     else:
          return None

print(strip_first_last("Hello World"))

[Peter]

Solution in Go:

package main

import (
    "fmt"
)

func main() {
    p, err := peel("hello")
    if err != nil {
        panic(err)
    }
    fmt.Println(p)
}

func peel(s string) (string, error) {
    if len(s) < 3 {
        return "", fmt.Errorf("Input string too short")
    }
    return s[1 : len(s)-1], nil
}

Running example in Go Playground

[Vivek]

Swift - 5

var str = "Hello, playground"
func stringPeeler(input: String) -> String? {
    if (input.count <= 2) {
        return nil;
    }

    return String(input.dropLast().dropFirst())
}

print(stringPeeler(input: str)!)

[Werner Echezuría]

Rust

fn trim_string(string: &str) -> &str {
    if string.len() <= 2 {
        panic!("Input string too short");
    }
    &string[1..string.len() - 1]
}

[kesprit]

Swift

func removeFirstAndLastLetter(value: String) -> String? {
    guard value.count > 3 else { return nil }
    var result = value.dropFirst()
    result.popLast()
    return String(result)
}

[Kyle Jones]

In Python:

def peel_string(text):
    if len(text) > 2:
        return text[1:(len(text) - 1)]
    return None

print(peel_string("Testing"))
print(peel_string("Hi"))
print(peel_string(""))

[Josh]

Trivial in Ruby:

def double_chop(string)
  return string if string.length <= 2
  string[1..-2]
end

double_chop("hello world") # => "ello worl"
double_chop("book")        # => "oo"
double_chop("OOP")         # => "O"
double_chop("hi")          # => "hi"

[Vinicius Cavagnolli]

VB5 / VB6

Function Challenge1(input As String) As String
    If len(input) <= 2 Then
        Challenge1 = Nothing
    Else
        Challenge1 = Mid$(input, 2, len(input) - 2) 
    End If
End Function

Visual Basic .NET

Function Challenge1(input as String)
    Return If(input.Length > 2, Mid(input, 2, len(input) - 2), Nothing)
End Function

C#

string Challenge1(string input) => input.Length > 2 ? input.Substring(1, input.Length - 2) : null;

C# using LINQ (because yes)

string Challenge1(string input) => input.Length > 2 ? string.Concat(input.Skip(1).Take(input.Length - 2)) : null;

[Shannon Crabill]

I liked today's challenge so I'm going back to do past ones

def string_peeler(string)
  if string.length > 2
    string.delete(string[0]).delete(string[-1])
  end
end

Returns

string_peeler("hi") => nil 
string_peeler("killer") => "ille" 
string_peeler("BOB") => "O"