Matt Ellen-Tsivintzeli

Posted on Nov 2, 2020 • Edited on Nov 13, 2020

Reverse a string: awful answers only

#challenge #programming #jokes

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('') == '';

Latest comments (18)

edh_developer • Nov 14 '20 • Edited

Go - convert the string to a slice of runes, swap the runes in the slice via some bit manipulation, then convert the slice back to string and return it.

Remember, to swap the values of two integers a and b...

a = a XOR b
b = a XOR b
a = a XOR b

func reverse(s string) string {
    characters := []rune(s)

    for i, j := 0, len(characters)-1; i < j; {
        characters[i] ^= characters[j]
        characters[j] ^= characters[i]
        characters[i] ^= characters[j]
        i++
        j--
    }

    return string(characters)
}

Update: it occurred to me that the solution above may be odd, but it's not that inefficient. We can do better. So... take 2:

type charNode struct {
    C rune
    I int
}

func sortNodes(nodes []charNode) {

    var cn charNode

    for outer := len(nodes) - 1; outer > 0; outer-- {
        for inner := len(nodes) - 1; inner > 0; inner-- {
            if nodes[inner].I > nodes[inner-1].I {
                cn = nodes[inner]
                nodes[inner] = nodes[inner-1]
                nodes[inner-1] = cn
            }
        }
    }

}

func reverseViaSort(s string) string {
    nodes := make([]charNode, len(s))

    for i, r := range []rune(s) {
        nodes[i] = charNode{r, i}
    }

    sortNodes(nodes)
    sortedRunes := make([]rune, len(s))
    for i, n := range nodes {
        sortedRunes[i] = n.C
    }

    return string(sortedRunes)
}

We split the string into a slice of ordered rune-index pairs, reverse the slice by sorting based on the indices, then get the resulting string from the reordered slice. It's pretty inefficient to begin with, and choosing bubblesort as our sorting algorithm gets us some O(N^2) fun.

Gary Bell • Nov 5 '20 • Edited

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!

Jason C. McDonald • Nov 3 '20

OOoooooooooooo, I love it! Bit late to this party (we'll see if I can get a terrible answer in later), but I hope you make a habit of posting these! My kind of challenge. :D

Junxiao Shi • Nov 3 '20

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(""))
}

Pontakorn Paesaeng • Nov 3 '20

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;
}

Michel Betancourt • Nov 3 '20 • Edited

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

Akash Kava • Nov 3 '20

Recursive reverse.

function reverse(s) {
if(!s) return “”;
return reverse(s.substring(1)) + s[0];
}

K. Russell Smith • Nov 2 '20 • Edited

#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 🎉

lionel-rowe • Nov 2 '20 • Edited

❤️ 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 • Nov 14 '20

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

y1s1h1 • Nov 2 '20

include

using namespace std;
int main(){
cout << "Syntax error";
return 0;
}

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