Reverse a string: awful answers only

Today's challenge is to write a function that when given a string returns the string with the characters in the reverse order.

E.g.

reverseString('hello');
//output: 'olleh'

But instead of trying to make a nice shiny function, write something bad. Throw space and time optimisations out the window. Double down on cyclomatic complexity. Make the compiler sad.

Tests

reverseString('Use Markdown to write and format posts.') == '.stsop tamrof dna etirw ot nwodkraM esU';
reverseString('You can use Liquid tags to add rich content such as Tweets, YouTube videos, etc.') == '.cte ,soediv ebuTuoY ,steewT sa hcus tnetnoc hcir dda ot sgat diuqiL esu nac uoY';
reverseString('In addition to images for the post\'s content, you can also drag and drop a cover image') == 'egami revoc a pord dna gard osla nac uoy ,tnetnoc s\'tsop eht rof segami ot noitidda nI';
reverseString('') == '';

Comments

[Guido Zuidhof]

Why not use Python's [::-1], but entirely in the browser? We can load the Pyodide runtime so we can run Python in the browser through WebAssembly. We'll have to eval as no ES module is shipped, but surely that's not a problem. Also the runtime is 20MB, but it's worth it!

var stringToReverse = "hello";

const reversed = new Promise((resolve) => {
    (async() => {
        const pyodideLoaderJS = await (await fetch("https://cdn.jsdelivr.net/pyodide/v0.15.0/full/pyodide.js")).text()
        await eval(pyodideLoaderJS)

        resolve(pyodide.runPython(`
            from js import stringToReverse;
            stringToReverse[::-1]
        `))
    })();
});

reversed.then(s => console.log(s));

Copy it into your browser console and be amazed..

[Nathan Kallman]

Just shuffle the characters and see if it reversed the string! We'll get the reverse eventually.... (prepare to wait a long time for strings longer than 8 characters)

function reverseString(string, maxIterations = 10000, verbose = false) {
  const originalString = string.split("");
  let shuffledString = string.split("");
  let isReverse;
  let iteration = 1;
  do {
    for (let i = 0; i < shuffledString.length; i++) {
      let j = Math.floor(Math.random() * (string.length - i) + i);
      if (i != j) {
        shuffledString[i] = shuffledString[i] + shuffledString[j];
        shuffledString[j] = shuffledString[i].replace(shuffledString[j], "");
        shuffledString[i] = shuffledString[i].replace(shuffledString[j], "");
      }
    }
    if (verbose) console.log("Candidate string: ", shuffledString.join(""));
    isReverse = true;
    for (let i = 0; i < shuffledString.length; i++) {
      isReverse = isReverse && originalString[i] == shuffledString[shuffledString.length - 1 - i];
    }
    iteration++;
  } while (!(isReverse || iteration > maxIterations));
  if (isReverse) {
    return shuffledString.join("");
  } else {
    return false;
  }
}

[Gil Fewster]

Perfect!

[mattother]

I'm loving this. Here my attempt:

// Reverses stuff.
function reverseString(y) {
    console.log('starting string reverse');
    console.warn('a string reverse is about to start'); q = esreveRgnirts(y);
    console.log('finished string reverse');
    return q
}

function esreveRgnirts (rts) {
  return xednIesreveRrts(rts, 0);
}

function xednIesreveRrts (rts, i) {
    if (i >= rts.length)
      return '';

  return tArahCteg(rts, rts.length - i - 1, 0) + xednIesreveRrts(rts, i+1);
}

function tArahCteg(rts, i, j) {
    if (i == j) {
        xeger = '^';
        for (q = 0; q < i; q++) {
            xeger += '.{1}';
        }
        xeger += "(.{1}).*$";
        r = new RegExp(xeger);
        return rts.match(r)[1];
    }
    return tArahCteg(rts, i, j + 1)
}

[Christopher Graves]

This is my favorite so far. The reversed signatures are a nice touch

[mattother]

Thanks! Felt very meta some how.

[Matt Ellen-Tsivintzeli]

My humble submission:

function reverseString(s)
{
  let rev = s;
  for(let i = 0; i < s.length-1; i++)
  {
    let p = `(.)(.{${s.length-1-i},${s.length-1-i}})(.{${i},${i}})`;
    rev = rev.replace(new RegExp(p), '$2$1$3');
  }
  return rev;
}

[lionel-rowe]

❤️ this challenge

This solution is inspired by my_first_calculator.py. It works for all lowercase alphabetic strings of length 3. The generated (non-evaled) version is 17,582 lines of code.

const reverse = eval(`str => {
${[...new Array(26).keys()].map(x =>
    [...new Array(26).keys()].map(y =>
        [...new Array(26).keys()].map(z =>
            [x, y, z]
                .map(n => String.fromCharCode(n + 'a'.charCodeAt(0)))
        )
    )
)
    .flat()
    .flat()
    .map(([x, y, z]) =>
        `    if (str === '${[x, y, z].join('')}') return '${[z, y, x].join('')}'`)
    .join('\n')}

    throw new RangeError(
        'Sorry, your string is not supported yet. Please try again in 3–6 months.'
    )
}`)

[Paul Hubert]

When I open the "my_first_calculator.py" file it took so long, I thought something was wront with the git site ou my internet was down. Then I saw the file and I understood

[Michel Betancourt]

so easy

function reverse(val: string) {
  if(val==='a'){
    return 'a'
  } else if(val==='aa') {
    return 'aa'
  } else if(....) {} // 75 years later
  else if (val === 'aucn') {
    return 'ncua'
  }  else if(....) {} // 2000 years later
  else if (val === 'asynchronous') {
    return 'suonorhcnysa'
  }
}
console.log(reverse('asynchronous'))

this works for any amount of chars xd

[Junxiao Shi]

We need a computer network.

package main

import (
    "fmt"
    "io/ioutil"
    "net/http"
    "strconv"
    "strings"
    "sync"
    "time"
)

func reverseString(s string) string {
    server := http.Server{
        Addr: ":8080",
        Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
            q := r.URL.Query()
            t, _ := strconv.Atoi(q.Get("t"))
            c, _ := strconv.Atoi(q.Get("c"))
            time.Sleep(time.Duration(len(s)-t) * 100 * time.Millisecond)
            w.Write([]byte{byte(c)})
        }),
    }
    go server.ListenAndServe()
    defer server.Close()
    time.Sleep(time.Second)

    client := http.Client{
        Timeout: time.Duration(len(s)) * time.Second,
    }
    var wg sync.WaitGroup
    var lock sync.Mutex
    var b strings.Builder
    for t, c := range []byte(s) {
        wg.Add(1)
        go func(t int, c byte) {
            defer wg.Done()
            res, e := client.Get(fmt.Sprintf("http://localhost:8080/?t=%d&c=%d", t, c))
            if e != nil {
                panic(e)
            }

            defer res.Body.Close()
            body, e := ioutil.ReadAll(res.Body)
            if e != nil {
                panic(e)
            }

            lock.Lock()
            defer lock.Unlock()
            b.Write(body)
        }(t, c)
    }

    wg.Wait()
    return b.String()
}

func main() {
    fmt.Println(reverseString("Use Markdown to write and format posts."))
    fmt.Println(reverseString("You can use Liquid tags to add rich content such as Tweets, YouTube videos, etc."))
    fmt.Println(reverseString("In addition to images for the post's content, you can also drag and drop a cover image"))
    fmt.Println(reverseString(""))
}

[K. Russell Smith]

#include <stdio.h>
#include <stdlib.h>
int len(const char*str)
{
    int result=0;
GETATIT:
    if (*(str+result++)=='\0') goto END;
    goto GETATIT;
END:
    return result;
}
char*reversed(const char* str)
{
    #define reset i=0
    char*result=(char*)malloc(sizeof(char)*len(str));
    int reset;
YOUCANDOIT:
    if ((*(result+len(str)-1-i)=*(str+i))=='\0')
        goto ONEMORESTEP;
    ++i;
    goto YOUCANDOIT;
ONEMORESTEP:
    reset;
    LOOP:
    *(result+i)=*(result+i+1);
    if (i++>=len(result)-1) goto WEDIDIT;
    goto LOOP;
WEDIDIT:
    *(result+i)='\0';
    return result;
}
int main(int argc, char*argv[])
{
    const char*str="Foo!";
    char*reverse=reversed(str);
    printf("%s\n",reverse);
    free(reverse);
    return 0;
}

WEDIDIT 🎉

[Pontakorn Paesaeng]

I am too lazy to implement the reverse function so I made cursed version instead.

#include <stdio.h>
// Credit: https://www.programmingsimplified.com/c-program-reverse-string
#define function int
#define main main() {
#define consolelog printf
#define Systemscanf gets
#define konodioda return
function main
   char s[1000], r[1000];
   int begin, end, count = 0;

   consolelog("Input a string\n");

   Systemscanf(s);

   // Calculating string length

   while (s[count] != '\0')
      count++;

   end = count - 1;

   for (begin = 0; begin < count; begin++) {
      r[begin] = s[end];
      end--;
   }

   r[begin] = '\0';

   consolelog("%s\n", r);

   konodioda 0;
}

[Gary Bell]

function reverseString(string $input): string
{
    $reverseCode = '';
    for ($i = strlen($input) -1; $i >= 0; $i--) {
        //$reverseCode .= 'substr("' . str_replace("'", "\'", $input) . '", ' . $i . ', 1) . ';
        $reverseCode .= 'substr(\"' . $input . '\", ' . $i . ', 1) . ';
    }
    $reverseCode .= '\"\";';
    $reversedString = exec("php -r \"echo $reverseCode\"");
    return $reversedString;
}

Ok, so this monstrosity uses the built-in substr method. But instead of using that to determine the string, it builds a whole bund of PHP code to execute within the shell, calls that via exec, and returns the string.

Awfully bad practice, inefficient, and dangerous. It's the type of code which gives PHP a bad name!