Problema:

Você deve criar um programa que faça o seguinte:

• pega uma grande sequência de texto em minúsculas e conta todas as ocorrências de cada letra.
• então você coloca as letras em ordem, da maior para a menor ocorrência.
• então você pega essa lista e a transforma em um codificador / decodificador para o texto.
• depois codifica o texto com essa cifra.

Dificíl de entender? Veja este exemplo:

Exemplo:

Entrada de texto:

Lorem ipsum dolor sente-se no meio, consectetur elip adipiscing. Nunc sed dui e nisi euismod pellentesque ac sed enim. Nullam auctor justo quis diam faucibus, eu fringilla é porttitor. Pellentesque vel pharetra nisl. O vestíbulo congela ultrices magna a fringilla. Quisque porttitor, risus suscipit pellentesque tristique, orci lorem accumsan nisi, scelerisque viverra turpis metus sit amet sapien. Fusce facilisis diam turpis, ne lobortis dui blandit ne. Vestibulum ac urna ut lacus commodo sollicitudin nec non velit. Nulla cursus urna sem, e tincidunt sem molestie vel. Nullam fringilla ante eu dolor bibendum, posuere iaculis nunc lacinia. Sed ac pretium est, vel scelerisque nisl. Phasellus lobortis dolor sodales sapien mollis hendrerit. Número inteiro temporário, viverra varius neque mattis in. et feugiat tortor tincidunt vel. Aenean dignissim eleifend faucibus. Morbi nec neque vel ante pulvinar mollis eu in ipsum.

Converter em minúsculas.

Contagem de caracteres (por letra. Espaços e pontuação ignorados):

[('a', 49), ('b', 11), ('c', 34), ('d', 22), ('e', 93), ('f', 9), ( 'g', 10), ('h', 3), ('i', 89), ('j', 1), ('k', 0), ('l', 61), ('m ', 31), (' n ', 56), (' o ', 37), (' p ', 20), (' q ', 12), (' r ', 47), (' s ', 71), ('t', 59), ('u', 65), ('v', 15), ('w', 0), ('x', 0), ('y', 0) , ('z', 0)]

Contagem de caracteres ordenada:

[('e', 93), ('i', 89), ('s', 71), ('u', 65), ('l', 61), ('t', 59), ( 'n', 56), ('a', 49), ('r', 47), ('o', 37), ('c', 34), ('m', 31), ('d ', 22), (' p ', 20), (' v ', 15), (' q ', 12), (' b ', 11), (' g ', 10), (' f ', 9), ('h', 3), ('j', 1), ('k', 0), ('w', 0), ('x', 0), ('y', 0) , ('z', 0)]

Em seguida, crie uma tabela de pesquisa usando as listas originais e classificadas:

abcdefghijklmnopqrstuvwxyz
||||||||||||||||||||||||||
eisultnarocmdpvqbgfhjkwxyz

Dicionário Python:

{'o': 'v', 'n': 'p', 'm': 'd', 'l': 'm', 'k': 'c', 'j': 'o', 'i': 'r', 'h': 'a', 'g': 'n', 'f': 't', 'e': 'l', 'd': 'u', 'c': 's', 'b': 'i', 'a': 'e', 'z': 'z', 'y': 'y', 'x': 'x', 'w': 'w', 'v': 'k', 'u': 'j', 't': 'h', 's': 'f', 'r': 'g', 'q': 'b', 'p': 'q'}

E agora codifique o texto original com esta tabela de pesquisa:

«Lvgld rqfjd uvmvg frh edlh, svpflshlhjg eurqrfsrpn lmrh. Njps gripe ujr eh prfr ljrfdvu qlmmlphlfbjl es gripe lprd. Njmmed ejshvg ojfhv bjrf ured tejsrijf, lj tgrpnrmme lfh qvghhrhvg. Plmmlphlfbjl klm qaeglhge prfm. Vlfhrijmjd svpnjl jmhgrslf denpe e tgrpnrmme. Qjrfbjl qvghhrhvg, grfjf fjfsrqrh qlmmlphlfbjl hgrfhrbjl, vgsr mvgld essjdfep prfr, fslmlgrfbjl krklgge hjgqrf dlhjf frh edlh feqrl. Fjfsl tesrmrfrf ured hjgqrf, pls mvivghrf ujr imepurh pls. Vlfhrijmjd es jgpe jh mesjf svddvuv fvmmrsrhjurp pls pvp klmrh. Njmme sjgfjf jgpe fld, eh hrpsrujph fld dvmlfhrl klm. Njmmed tgrpnrmme ephl lj uvmvg irilpujd, qvfjlgl resjmrf pjps mesrpre. Slu es qglhrjd lfh, klm fslmlgrfbjl prfm. Paeflmmjf mvivghrf uvmvg fvuemlf feqrlp dvmmrf alpuglgrh. Iphlnlg fslmlgrfbjl hldqvg hlmmjf, krklgge kegrjf plbjl dehhrf rp. Iphlnlg qvghe klfhrijmjd prfm, lh tljnreh hvghvg hrpsrujph klm. Alplep urnprffrd lmlrtlpu tejsrijf. Mvgir pls plbjl klm ephl qjmkrpeg dvmmrf lj rp rqfjd. '

Eu amo python!

Regras:

• Seu programa aceitará uma string e emitirá uma.
• Converta todas as entradas em minúsculas antes de fazer qualquer coisa
• Não me importo como você classifica a lista, mas conta apenas letras minúsculas
• Pontos de bônus (-30) por criar um decodificador (sem copiar a lista de decodificação), faça-o do zero
• Isto é código-golfe, então o código mais curto vence!
• Diverta-se!

GolfScript, 39 caracteres

:I{97,26,{97+}%{[.32-]I\-,}$+'{|}~'+=}%

Versão online para teste. Observe que a classificação não é definida se vários caracteres tiverem a mesma contagem na sequência de entrada.

Saída de exemplo

Lvgld rqfjd uvmvg frh edlh, svpflshlhjg eurqrfsrpn lmrh. Njps gripe ujr eh prfr ljrfdvu qlmmlphlfbjl es gripe lprd. Njmmed ejshvg ojfhv bjrf ured tejsrijf, lj tgrpnrmme lfh qvghhrhvg. Plmmlphlfbjl wlm qaeglhge prfm. Vlfhrijmjd svpnjl jmhgrslf denpe e tgrpnrmme. Qjrfbjl qvghhrhvg, grfjf fjfsrqrh qlmmlphlfbjl hgrfhrbjl, vgsr mvgld essjdfep prfr, fslmlgrfbjl wrwlgge hjgqrf dlhjf frh edlh feqrlp. Fjfsl tesrmrfrf ured hjgqrf, pls mvivghrf ujr imepurh pls. Vlfhrijmjd es jgpe jh mesjf svddvuv fvmmrsrhjurp pls pvp wlmrh. Njmme sjgfjf jgpe fld, eh hrpsrujph fld dvmlfhrl wlm. Njmmed tgrpnrmme ephl lj uvmvg irilpujd, qvfjlgl resjmrf pjps mesrpre. Slu es qglhrjd lfh, wlm fslmlgrfbjl prfm. Paeflmmjf mvivghrf uvmvg fvuemlf feqrlp dvmmrf alpuglgrh. Iphlnlg fslmlgrfbjl hldqvg hlmmjf, wrwlgge wegrjf plbjl dehhrf rp. Iphlnlg qvghe wlfhrijmjd prfm, lh tljnreh hvghvg hrpsrujph wlm. Alplep urnprffrd lmlrtlpu tejsrijf. Mvgir pls plbjl wlm ephl qjmwrpeg dvmmrf lj rp rqfjd.

Bash / coreutils, 91 caracteres

tr a-z `echo {a..z} $1|fold -w1|grep '[a-z]'|sort|uniq -c|sort -rn|awk '{printf $2}'`<<<$1

Salve como cipher.sh, chmod + xe execute:

$ ./cipher.sh "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc sed dui at nisi euismod pellentesque ac sed enim. Nullam auctor justo quis diam faucibus, eu fringilla est porttitor. Pellentesque vel pharetra nisl. Vestibulum congue ultrices magna a fringilla. Quisque porttitor, risus suscipit pellentesque tristique, orci lorem accumsan nisi, scelerisque viverra turpis metus sit amet sapien. Fusce facilisis diam turpis, nec lobortis dui blandit nec. Vestibulum ac urna ut lacus commodo sollicitudin nec non velit. Nulla cursus urna sem, at tincidunt sem molestie vel. Nullam fringilla ante eu dolor bibendum, posuere iaculis nunc lacinia. Sed ac pretium est, vel scelerisque nisl. Phasellus lobortis dolor sodales sapien mollis hendrerit. Integer scelerisque tempor tellus, viverra varius neque mattis in. Integer porta vestibulum nisl, et feugiat tortor tincidunt vel. Aenean dignissim eleifend faucibus. Morbi nec neque vel ante pulvinar mollis eu in ipsum."
Lvgld rqfjd uvmvg frh edlh, svpflshlhjg eurqrfsrpn lmrh. Njps flu ujr eh prfr ljrfdvu qlmmlphlfbjl es flu lprd. Njmmed ejshvg ojfhv bjrf ured tejsrijf, lj tgrpnrmme lfh qvghhrhvg. Plmmlphlfbjl jlm qaeglhge prfm. Vlfhrijmjd svpnjl jmhgrslf denpe e tgrpnrmme. Qjrfbjl qvghhrhvg, grfjf fjfsrqrh qlmmlphlfbjl hgrfhrbjl, vgsr mvgld essjdfep prfr, fslmlgrfbjl jrjlgge hjgqrf dlhjf frh edlh feqrlp. Fjfsl tesrmrfrf ured hjgqrf, pls mvivghrf ujr imepurh pls. Vlfhrijmjd es jgpe jh mesjf svddvuv fvmmrsrhjurp pls pvp jlmrh. Njmme sjgfjf jgpe fld, eh hrpsrujph fld dvmlfhrl jlm. Njmmed tgrpnrmme ephl lj uvmvg irilpujd, qvfjlgl resjmrf pjps mesrpre. Slu es qglhrjd lfh, jlm fslmlgrfbjl prfm. Paeflmmjf mvivghrf uvmvg fvuemlf feqrlp dvmmrf alpuglgrh. Iphlnlg fslmlgrfbjl hldqvg hlmmjf, jrjlgge jegrjf plbjl dehhrf rp. Iphlnlg qvghe jlfhrijmjd prfm, lh tljnreh hvghvg hrpsrujph jlm. Alplep urnprffrd lmlrtlpu tejsrijf. Mvgir pls plbjl jlm ephl qjmjrpeg dvmmrf lj rp rqfjd.
$ 

Rubi, 104 92 91 caracteres

Guardou muitos caracteres graças a @Chron

f=->(s){m=[*?a..?z];l=m.map{|x|[-s.downcase.count(x),x]};s.tr(m*'',l.sort.transpose[1]*'')}

Versão Online aqui. A classificação de caracteres com a mesma contagem não está definida, conforme mencionado em outra resposta. Com a entrada "asdf", cada resposta tem outra saída até o momento.

Em outras palavras: todas as respostas têm o mesmo comportamento (portanto representam uma codificação decodificável) quando a entrada contém o alfabeto inteiro com cada letra tendo uma contagem exclusiva.

Mathematica 171

f@m_:=StringReplace[m,Thread[(CharacterRange["a",
FromCharacterCode[96+Length@(l=Reverse@SortBy[Tally[Select[Characters@m,
(LetterQ@#\[And]LowerCaseQ@#)&]],Last][[All,1]])]])->l ]]

Supondo que té o texto Lorem ipsum.

f[t]

"Lvgld rqfjd uvmvg FRH edlh, svpflshlhjg eurqrfsrpn lmrh.Njps gripe RJU eh prfr ljrfdvu qlmmlphlfbjl es gripe lprd.Njmmed ejshvg ojfhv bjrf ured tejsrijf, lj tgrpnrmme LFH qvghhrhvg.Plmmlphlfbjl VLM qaeglhge prfm.Vlfhrijmjd svpnjl jmhgrslf denpe e tgrpnrmme.Qjrfbjl qvghhrhvg, grfjf fjfsrqrh qlmmlphlfbjl hgrfhrbjl, vgsr mvgld essjdfep prfr, fslmlgrfbjl vrvlgge hjgqrf dlhjf FRH edlh feqrlp.Fjfsl tesrmrfrf ured hjgqrf, pls mvivghrf RJU imepurh pls.Vlfhrijmjd es jgpe jh mesjf svddvuv fvmmrsrhjurp pls pvp vlmrh.Njmme sjgfjf jgpe fld, eh hrpsrujph fld dvmlfhrl VLM. Njmmed tgrpnrmme ephl lj uvmvg irilpujd, qvfjlgl resjmrf pjps mesrpre.Slu es qglhrjd LFH, VLM fslmlgrfbjl prfm.Paeflmmjf mvivghrf uvmvg fvuemlf feqrlp dvmmrf alpuglgrh.Iphlnlg fslmlgrfbjl hldqvg hlmmjf, vrvlgge vegrjf plbjl dehhrf rp.Iphlnlg qvghe vlfhrijmjd prfm,lh tljnreh hvghvg hrpsrujph vlm.Alplep urnprffrd lmlrtlpu tejsrijf.

As regras de substituição geradas por Thread…-> lforam:

{"a" -> "e", "b" -> "i", "c" -> "s", "d" -> "u", "e" -> "l", "f" - > "t", "g" -> "n", "h" -> "a", "i" -> "r", "j" -> "o", "k" -> "c", "l" -> "m", "m" -> "d", "n" -> "p", "o" -> "v", "p" -> "q", "q" -> "b", "r" -> "g", "s" -> "f", "t" -> "h", "u" -> "j"}

K, 43

{x^(b!b^26$>#:'=a@&(a:_x)in b:"c"$97+!26)x}

C # 386

using System.Collections.Generic;using System.Linq;namespace N{class P{static void Main(string[]a){char[] f="abcdefghijklmnopqrstuvwxyz".ToCharArray();Dictionary<char,int>l=new Dictionary<char,int>();foreach (char c in f) l.Add(c, "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc sed dui at nisi euismod pellentesque ac sed enim. Nullam auctor justo quis diam faucibus, eu fringilla est porttitor. Pellentesque vel pharetra nisl. Vestibulum congue ultrices magna a fringilla. Quisque porttitor, risus suscipit pellentesque tristique, orci lorem accumsan nisi, scelerisque viverra turpis metus sit amet sapien. Fusce facilisis diam turpis, nec lobortis dui blandit nec. Vestibulum ac urna ut lacus commodo sollicitudin nec non velit. Nulla cursus urna sem, at tincidunt sem molestie vel. Nullam fringilla ante eu dolor bibendum, posuere iaculis nunc lacinia. Sed ac pretium est, vel scelerisque nisl. Phasellus lobortis dolor sodales sapien mollis hendrerit. Integer scelerisque tempor tellus, viverra varius neque mattis in. Integer porta vestibulum nisl, et feugiat tortor tincidunt vel. Aenean dignissim eleifend faucibus. Morbi nec neque vel ante pulvinar mollis eu in ipsum.".ToLower().Trim().Count(v => v == c));foreach (KeyValuePair<char, int> i in l.OrderByDescending(p => p.Value))System.Console.Write(i.Key +""+i.Value);}}}

Descomprimido.

using System.Collections.Generic;
using System.Linq;
namespace N {
    class P {
        static void Main(string[]a){
            char[] f="abcdefghijklmnopqrstuvwxyz".ToCharArray();
            Dictionary<char,int>l=new Dictionary<char,int>();
            foreach (char c in f) 
                l.Add(c, "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc sed dui at nisi euismod pellentesque ac sed enim. Nullam auctor justo quis diam faucibus, eu fringilla est porttitor. Pellentesque vel pharetra nisl. Vestibulum congue ultrices magna a fringilla. Quisque porttitor, risus suscipit pellentesque tristique, orci lorem accumsan nisi, scelerisque viverra turpis metus sit amet sapien. Fusce facilisis diam turpis, nec lobortis dui blandit nec. Vestibulum ac urna ut lacus commodo sollicitudin nec non velit. Nulla cursus urna sem, at tincidunt sem molestie vel. Nullam fringilla ante eu dolor bibendum, posuere iaculis nunc lacinia. Sed ac pretium est, vel scelerisque nisl. Phasellus lobortis dolor sodales sapien mollis hendrerit. Integer scelerisque tempor tellus, viverra varius neque mattis in. Integer porta vestibulum nisl, et feugiat tortor tincidunt vel. Aenean dignissim eleifend faucibus. Morbi nec neque vel ante pulvinar mollis eu in ipsum.".ToLower().Trim().Count(v => v == c));
            foreach (KeyValuePair<char, int> i in l.OrderByDescending(p => p.Value))
                System.Console.Write(i.Key +""+i.Value);
        }
    }
}

PHP, 151

^{(com configuração short_open_tag = On)}

<?$c=array_slice(count_chars(strtolower($s=$argv[1])),97,26,1);arsort($c);echo strtr($s,array_combine(range('a','z'),array_map('chr',array_keys($c))));

Isso espera que o texto seja o primeiro argumento para o script. Igual a:

php cypher.php "Lorem ipsum [...]"

R, 137

l=letters;s=strsplit(readline(),"")[[1]];g=grep("[a-z]",s);s[g]=names(sort(table(factor(tolower(s),l)),d=T))[match(s[g],l)];cat(s,sep="")

Saída (com base no exemplo em questão):

Lvgld rqfjd uvmvg frh edlh, svpflshlhjg eurqrfsrpn lmrh. Njps gripe ujr eh prfr ljrfdvu qlmmlphlfbjl es gripe lprd. Njmmed ejshvg ojfhv bjrf ured tejsrijf, lj tgrpnrmme lfh qvghhrhvg. Plmmlphlfbjl klm qaeglhge prfm. Vlfhrijmjd svpnjl jmhgrslf denpe e tgrpnrmme. Qjrfbjl qvghhrhvg, grfjf fjfsrqrh qlmmlphlfbjl hgrfhrbjl, vgsr mvgld essjdfep prfr, fslmlgrfbjl krklgge hjgqrf dlhjf frh edlh feqrl. Fjfsl tesrmrfrf ured hjgqrf, pls mvivghrf ujr imepurh pls. Vlfhrijmjd es jgpe jh mesjf svddvuv fvmmrsrhjurp pls pvp klmrh. Njmme sjgfjf jgpe fld, eh hrpsrujph fld dvmlfhrl klm. Njmmed tgrpnrmme ephl lj uvmvg irilpujd, qvfjlgl resjmrf pjps mesrpre. Slu es qglhrjd lfh, klm fslmlgrfbjl prfm. Paeflmmjf mvivghrf uvmvg fvuemlf feqrlp dvmmrf alpuglgrh. Iphlnlg fslmlgrfbjl hldqvg hlmmjf, krklgge kegrjf plbjl dehhrf rp. Iphlnlg qvghe klfhrijmjd prfm, lh tljnreh hvghvg hrpsrujph klm. Alplep urnprffrd lmlrtlpu tejsrijf. Mvgir pls plbjl klm ephl qjmkrpeg dvmmrf lj rp rqfjd.

Smalltalk, 138

entrada em s:

m:=(s select:[:c|cisLetter])asLowercase asBag sortedCounts map:#value.
i:=($ato:$z).m:=m,(i copyWithoutAll:m).
s copyTransliterating:i to:m

o decodificador é:

s copyTransliterating:m to:i

mas como (se entendi corretamente) não posso reutilizar "i" e "m", vou jogar sem ele. O código acima tem dois CRs adicionais inseridos para facilitar a leitura, que não foram contados na contagem de caracteres.

Clojure, 135

(Supondo que o texto de entrada esteja contido no var s)

(let[a(map char(range 97 123))m(->> s .toLowerCase frequencies(sort-by val >)keys(filter(set a))(zipmap a))](apply str(map #(m % %)s)))

Python 2.7 (147)

Não é o código mais curto, mas como o Python ainda não está representado e como eu vejo "Eu amo o python!" na configuração do problema, aqui vou eu,

import sys;s=sys.argv[1];a=map(chr,range(97,123));print"".join([sorted(a,key=lambda x:-s.lower().count(x))[ord(c)-97]if c in a else c for c in s])

Espera que a sequência de entrada seja passada através da linha de comando. (o número de caracteres é reduzido para 122 se a sequência de entrada foi inserida magicamente na variável "s")

a=map(chr,range(97,123));print"".join([sorted(a,key=lambda x:-s.lower().count(x))[ord(c)-97]if c in a else c for c in s])

Ouput

Lvgld rqfjd uvmvg frh edlh, svpflshlhjg eurqrfsrpn lmrh. Njps gripe ujr eh prfr ljrfdvu qlmmlphlfbjl es gripe lprd. Njmmed ejshvg ojfhv bjrf ured tejsrijf, lj tgrpnrmme lfh qvghhrhvg. Plmmlphlfbjl klm qaeglhge prfm. Vlfhrijmjd svpnjl jmhgrslf denpe e tgrpnrmme. Qjrfbjl qvghhrhvg, grfjf fjfsrqrh qlmmlphlfbjl hgrfhrbjl, vgsr mvgld essjdfep prfr, fslmlgrfbjl krklgge hjgqrf dlhjf frh edlh feqrl. Fjfsl tesrmrfrf ured hjgqrf, pls mvivghrf ujr imepurh pls. Vlfhrijmjd es jgpe jh mesjf svddvuv fvmmrsrhjurp pls pvp klmrh. Njmme sjgfjf jgpe fld, eh hrpsrujph fld dvmlfhrl klm. Njmmed tgrpnrmme ephl lj uvmvg irilpujd, qvfjlgl resjmrf pjps mesrpre. Slu es qglhrjd lfh, klm fslmlgrfbjl prfm. Paeflmmjf mvivghrf uvmvg fvuemlf feqrlp dvmmrf alpuglgrh. Iphlnlg fslmlgrfbjl hldqvg hlmmjf, krklgge kegrjf plbjl dehhrf rp. Iphlnlg qvghe klfhrijmjd prfm, lh tljnreh hvghvg hrpsrujph klm. Alplep urnprffrd lmlrtlpu tejsrijf. Mvgir pls plbjl klm ephl qjmkrpeg dvmmrf lj rp rqfjd.

Perl, 84

$c{$_}++for lc($_=<>)=~/./g;@h{a..z}=sort{$c{$b}-$c{$a}}a..z;s/[a-z]/$h{$&}/ge;print

.

perl cipher.pl

.. entrada ignorada ..

Lvgld rqfjd uvmvg frh edlh, svpflshlhjg eurqrfsrpn lmrh. Njps gripe ujr eh prfr lj rfdvu qlmmlphlfbjl es gripe lprd. Njmmed ejshvg ojfhv bjrf ured tejsrijf, lj tgrpn rmme lfh qvghhrhvg. Plmmlphlfbjl klm qaeglhge prfm. Vlfhrijmjd svpnjl jmhgrslf dpepe e tgrpnrmme. Qjrfbjl qvghhrhvg, grfjf fjfsrqrh qlmmlphlfbjl hgrfhrbjl, vgsr mvgld essjdfep prfr, fslmlgrfbjl krklgge hjgqrf dlhjf frh edlh feqrl. Fjfsl te srmrfrf ured hjgqrf, pls mvivghrf ujr imepurh pls. Vlfhrijmjd es jgpe jh mesjf s vddvuv fvmmrsrhjurp pls pvp klmrh. Njmme sjgfjf jgpe fld, eh hrpsrujph fld dvmlf hrl klm. Njmmed tgrpnrmme ephl lj uvmvg irilpujd, qvfjlgl resjmrf pjps mesrpre. Slu es qglhrjd lfh, klm fslmlgrfbjl prfm. Paeflmmjf mvivghrf uvmvg fvuemlf feqrl p dvmmrf alpuglgrh. Iphlnlg fslmlgrfbjl hldqvg hlmmjf, krklgge kegrjf plbjl dehh rf rp. Iphlnlg qvghe klfhrijmjd prfm, lh tljnreh hvghvg hrpsrujph klm. Alplep ur nprffrd lmlrtlpu tejsrijf. Mvgir pls plbjl klm ephl qjmkrpeg dvmmrf lj rp rqfjd.

PS Foi uma piada, sobre decifrar? Ou devo reivindicar 30 bônus por provar que é impossível? É aabdecifrado para aabou bba? Ou babaca, era cacabaou ababcbno original, ou em babacasi, literalmente?

C # - 393 bytes

string e(string i){char[] f="abcdefghijklmnopqrstuvwxyz".ToCharArray();Dictionary<char,int>l=new Dictionary<char,int>();foreach (char c in f) l.Add(c, i.ToLower().Count(v => v == c));var w = (l.OrderByDescending(p => p.Value)).ToDictionary(q=>q.Key, y=>y.Value);var z = w.Keys.ToList();string r = "";foreach(char c in i) {if((int)c <=97 || (int)c>=122)r+=c;else r += z[((int)c-97)];}return r;}

A versão estendida da resposta de @ PauloHDSousa …