Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của flashmt

var test,it,m,n:longint; k,re:int64;
    c:char;
    s:string;
    d,dau:array['a'..'z'] of longint;

procedure rf;
var z:char;
begin
     readln(n,m);
     read(c); s:=''; k:=0; 
     if c='P' then
     begin
          read(z); readln(s);
     end
     else readln(k);
end;

function check:boolean;
var i:longint;
begin
     check:=false;
     fillchar(dau,sizeof(dau),0);
     for i:=1 to m do
         if (ord(s[i])>96+n) or (dau[s[i]]=1) then exit
         else dau[s[i]]:=1;
     check:=true;
end;

function calc(x,y:longint):int64;
var i:longint; r:int64;
begin
     r:=1;
     for i:=1 to x do r:=r*(y-i+1);
     calc:=r;
end;

procedure pr;
var i,t:longint; j:char;
begin
     if not check then writeln('Incorrect data')
     else
     begin
          fillchar(d,sizeof(d),0);
          re:=1;
          for i:=1 to m do
          begin
               t:=0;
               for j:='a' to s[i] do
                   if d[j]=0 then inc(t);
               if t>1 then re:=re+calc(m-i,n-i)*(t-1);
               d[s[i]]:=1;
          end;
          if re<=2000000000 then writeln(re) else writeln('Incorrect data');
     end;
end;

function check1:boolean;
var i:longint; x:int64;
begin
     check1:=true;
     x:=1;
     for i:=1 to m do
         if x>=k then exit else x:=x*(n-i+1);
     check1:=x>=k;
end;

function small(x,y:longint;var u:int64):boolean;
var i:longint; r:int64;
begin
     small:=true; r:=1; 
     for i:=1 to x do
         if r>=k then exit
         else r:=r*(y-i+1);
     if r<k then
     begin
          small:=false; u:=r;
     end;
end;

procedure pr1;
var i:longint; z:char; t,u:int64;
begin
     if not check1 then writeln('Incorrect data')
     else
     begin
          fillchar(d,sizeof(d),0);
          s:='';
          for i:=1 to m do
          begin
               if small(m-i,n-i,u) then t:=1
               else
               begin
                    t:=(k+u-1) div u;
                    k:=(k-1) mod u+1;
               end;
               z:=#96;
               while t>0 do
               begin
                    inc(z);
                    if d[z]=0 then dec(t);
               end;
               s:=s+z;
               d[z]:=1;
          end;
          writeln(s);
     end;
end;

begin
     readln(test);
     for it:=1 to test do
     begin
          rf;
          if c='P' then pr
          else pr1;
     end;
end.

Code mẫu của ladpro98

program NKLEXIC;
uses    math;
const   lim = 2*trunc(1e15);
        fi = '';
var     a:string;
        chk:array[1..30] of boolean;
        Akn:array[0..30,0..30] of int64;
        P:array[0..30] of longint;
        inp:text; c:char;
        n,m,t,tt,res,k:longint;

function ok(i: longint): boolean;
begin
        if (chk[i]) or (i>n) then exit(false);
        chk[i] := true;
end;

procedure Init;
var     n,k:longint;
begin
        for n:=1 to 26 do begin
                Akn[0,n]:=1; Akn[1,n] := n;
                for k:=2 to n do begin
                        Akn[k,n] := Akn[k-1,n]*(n - k + 1);
                        if Akn[k,n] > lim then break;
                end;
        end;
end;

function GetLexic:longint;
var     i, j, t, S:longint;
begin
        for i:=1 to n do chk[i]:=false;
        for i:=1 to m do begin
                P[i] := ord(a[i]) - ord('a') + 1;
                if not ok(P[i]) then exit(-1);
        end;
        S := 0;
        for i:=1 to n do chk[i]:=false;
        for i:=1 to m do begin
                t := 0;
                for j:=1 to P[i]-1 do if not chk[j] then inc(t);
                inc(S, t * Akn[m - i, n - i]);
                chk[P[i]] := true;
        end;
        exit(S+1);
end;

procedure GetStr(k: longint; var a:string);
var     i,j,v,t:longint;
begin
        a:='';
        if (k>Akn[m,n]) or (k>lim) then begin a := 'Incorrect data'; exit; end;
        for i:=1 to n do chk[i] := false;
        for i:=1 to m do begin
                for j := n-1 downto 0 do begin
                        t := 0;
                        for v:=1 to j do
                        if not chk[v] then inc(t);
                        if (not chk[j+1]) and (t*Akn[m-i, n-i] < k) then break;
                end;
                a := a + chr(j+ord('a'));
                chk[j+1] := true;
                dec(k, t*Akn[m-i, n-i]);
        end;
end;

begin
        Init;
        assign(inp,fi);reset(inp);
        readln(inp,t);
        for tt:=1 to t do begin
                readln(inp,n,m);
                read(inp,c);
                if c = 'P' then begin
                        read(inp,c,a);
                        res := GetLexic;
                        if res > 0 then
                        writeln(res)
                        else writeln('Incorrect data');
                end
                else begin
                        readln(inp,k);
                        GetStr(k, a);
                        writeln(a);
                end;
        end;
end.

Code mẫu của RR

{$R+,Q+}
{$Mode objFPC}
uses math;
const
  FINP          =       '';
  FOUT          =       '';
  MAXM          =       30;
  cc            :       string[26]='abcdefghijklmnopqrstuvwxyz';
  base          =       100000000;
  lbase         =       8;

var
  f1,f2:text;

type
  big           =       array[0..10] of int64;
  operator + (a,b:big) c:big;
  var
    i,nho:longint;
  begin
    nho:=0;
    fillchar(c,sizeof(c),0);
    c[0]:=max(a[0],b[0]);
    for i:=1 to c[0] do
      begin
        c[i]:=a[i]+b[i]+nho;
        if c[i]<base then nho:=0 else
        begin nho:=1; c[i]-=base; end;
      end;
    if nho>0 then
      begin
        inc(c[0]);
        c[c[0]]:=nho;
      end;
  end;
  operator - (a,b:big) c:big;
  var
    i,nho:longint;
  begin
    nho:=0;
    fillchar(c,sizeof(c),0);
    c[0]:=a[0];
    for i:=1 to c[0] do
      begin
        c[i]:=a[i]-b[i]-nho;
        if c[i]>=0 then nho:=0
        else begin nho:=1; c[i]+=base; end;
      end;
    while (c[0]>0) and (c[c[0]]=0) do dec(c[0]);
  end;
  operator * (a:big; k:longint) c:big;
  var
    i,nho:longint;
  begin
    nho:=0;
    fillchar(c,sizeof(c),0);
    c[0]:=a[0];
    for i:=1 to c[0] do
      begin
        c[i]:=a[i]*k+nho;
        if c[i]<base then nho:=0
        else begin nho:=c[i] div base; c[i]:=c[i] mod base; end;
      end;
    if nho>0 then
      begin
        inc(c[0]);
        c[c[0]]:=nho;
      end;
  end;
  operator < (a,b:big) c:boolean;
  var
    i:longint;
  begin
    if a[0]<b[0] then exit(true)
    else if a[0]>b[0] then exit(false);
    for i:=a[0] downto 1 do
      if a[i]<b[i] then exit(true)
      else if a[i]>b[i] then exit(false);
    exit(false);
  end;
  procedure print(var a:big);
  var
    i:longint;
    s:string;
  begin
    write(f2,a[a[0]]);
    for i:=a[0]-1 downto 1 do
      begin
        str(a[i],s);
        while length(s)<lbase do s:='0'+s;
        write(f2,s);
      end;
    writeln(f2);
  end;

var
  xet,a:array[0..MAXM*2] of longint;
  c:array[0..MAXM*2,0..MAXM*2+1] of big;
  tt:big;
  n,k:longint;

procedure openF;
    begin
      assign(f1,FINP); reset(f1);
      assign(f2,FOUT); rewrite(f2);
    end;
procedure closeF;
    begin
      close(f1); close(f2);
    end;

procedure init;
    var
      i,j:longint;
    begin
      for i:=0 to MAXM do
        begin
          c[i,0][0]:=1;   c[i,0][1]:=1;
          c[i,i+1][0]:=1; c[i,i+1][1]:=1;
        end;
      for i:=0 to MAXM do
      for j:=1 to i do
          c[i,j]:=c[i,j-1]*(i-j+1);
    end;
procedure solve1;
    var
      s:string;
      u,i:longint;
    begin
      fillchar(a,sizeof(a),0);
      fillchar(xet,sizeof(xet),0);
      for i:=1 to k do
        begin
          u:=1; while xet[u]=1 do inc(u);
          while (c[n-i,k-i]<tt) do
            begin
              tt:=tt-c[n-i,k-i];
              inc(u); while xet[u]=1 do inc(u);
            end;
          xet[u]:=1; a[i]:=u;
        end;
      for i:=1 to k do
        write(f2,cc[a[i]]);
      writeln(f2);
    end;
procedure solve2;
    var
      i,u:longint;
    begin
      fillchar(xet,sizeof(xet),0);
      fillchar(tt,sizeof(tt),0); tt[0]:=1; tt[1]:=1;
      xet[0]:=1;
      for i:=1 to k do
        begin
          u:=1; while xet[u]=1 do inc(u);
          while (u<a[i]) do
            begin
              if xet[u]=0 then tt:=tt+c[n-i,k-i];
              inc(u);
            end;
          xet[a[i]]:=1;
        end;
      print(tt);
    end;
var
  ok:boolean;
  l,test,i,j:longint;
  s:string;
  ch:char;
begin
  openF;
  init;
  readln(f1,test);
  for test:=1 to test do
    begin
      readln(f1,n,k);
      read(f1,ch);
      if ch='P' then
        begin
          read(f1,ch); readln(f1,s);
          while pos(' ',s)>0 do delete(s,pos(' ',s),1);
          for i:=1 to length(s) do
            a[i]:=pos(s[i],cc);
          ok:=true;
          l:=length(s);
          for i:=1 to l do
            if (a[i]<=0) or (a[i]>n) then ok:=false;
          for i:=length(s) downto 2 do
            for j:=i-1 downto 1 do
              if s[i]=s[j] then ok:=false;
          if (n<1) or (n>26) or (k<1) or (k>n) or (length(s)<>k) then ok:=false;
          if not ok then begin writeln(f2,'Incorrect data'); continue; end;
          solve2;
        end
      else
        begin
          read(f1,ch);
          fillchar(tt,sizeof(tt),0);
          readln(f1,tt[1]); tt[0]:=1;
          if tt[1]>base then begin tt[2]:=tt[1] div base; tt[1]:=tt[1] mod base; inc(tt[0]); end;
          if (c[n,k]<tt) or (n<1) or (n>26) or (k<1) or (k>n) then
            begin writeln(f2,'Incorrect data'); continue; end;
          solve1;
        end;
    end;
  closeF;
end.

Code mẫu của ll931110

Program NKLEXIC;
        Const
                input  = '';
                output = '';
        Var
                fi,fo: text;
                k,n,m: longint;

Procedure openfile;
          Begin
                Assign(fi, input);
                        Reset(fi);

                Assign(fo, output);
                        Rewrite(fo);
          End;

Procedure solveP;
          Var
                               s: string;
                      i,calc,x,j: longint;
                           val,p: qword;
                            Free: array[1..26] of boolean;
          Begin
                Readln(fi, s);
                Delete(s, 1, 1);
                Fillchar(Free, sizeof(Free), true);

                val:= 1;
                For i:= 1 to m do
                        Begin
                                x:= ord(s[i]) - 96;

                                If (x > n) or (Free[x] = false) then
                                        Begin
                                                Writeln(fo, 'Incorrect data');
                                                exit;
                                        End;

                                calc:= 0;

                                Free[x]:= false;
                                For j:= 1 to x do if Free[j] then inc(calc);

                                if calc <> 0 then
                                        Begin
                                                p:= 1;
                                                For j:= n - m + 1 to n - i do p:= p * j;
                                                val:= val + qword(calc) * p;
                                        End;

                        End;

                Writeln(fo, val);
          End;

Procedure solveW;
          Var
                      s: string;
              i,j,t,x,y: longint;
                val,inp: qword;
                   Free: array[1..26] of boolean;
          Begin
                Readln(fi, inp);
                Fillchar(Free, sizeof(Free), true);
                s:= '';

                For i:= 1 to m do
                        Begin
                                val:= 1;
                                For j:= n - m + 1 to n - i do
                                        Begin
                                                val:= val * j;
                                                if val > 2000000000 then break;
                                        End;

                                t:= inp div val;
                                If inp mod val = 0 then dec(t);

                                If t >= n then
                                        Begin
                                                Writeln(fo, 'Incorrect data');
                                                exit;
                                        End;

                                inp:= inp - val * t;

                                x:= 0;
                                y:= 0;

                                While x < t + 1 do
                                        Begin
                                                inc(y);
                                                If Free[y] then inc(x);
                                        End;

                                Free[y]:= false;
                                s:= s + chr(y + 96);
                        End;

                Writeln(fo, s);
          End;

Procedure printresult;
          Var
                i: longint;
               ch: char;
          Begin
                Readln(fi, k);

                For i:= 1 to k do
                        Begin
                                Readln(fi, n, m);
                                Read(fi, ch);
                                If ch = 'P' then solveP else solveW;
                        End;
          End;

Procedure closefile;
          Begin
                Close(fo);
                Close(fi);
          End;

Begin
        openfile;
        printresult;
        closefile;
End.

Code mẫu của khuc_tuan

#include <iostream>
using namespace std;

const long long MAXC = 4000000000LL;

int n, m;

long long tinh(int n, int m) {
    long long tmp = 1;
    for(int i=n-m+1;i<=n;++i) {
        tmp *= i;
        if(tmp>=MAXC) tmp = MAXC;
    }
    return tmp; 
}

void process( char * a ) {
    bool b[26];
    int na = strlen(a);
    memset( b, 0, sizeof(b));
    if(na!=m) {
        cout << "Incorrect data" << endl;
        return;
    }
    for(int i=0;i<na;++i) 
        if(a[i]>=n+'a' || a[i]<'a' || b[a[i]-'a']) {
            cout << "Incorrect data" << endl;
            return;
        }
        else b[a[i]-'a'] = true;

    memset( b, 0, sizeof(b));
    int res = 0;
    for(int i=0;i<na;++i) {
        for(int c=0;c<n;++c) {
            if(c==a[i]-'a') break;
            if(!b[c]) res += tinh( n-i-1, m-i-1);
        }
        b[a[i]-'a'] = true;
    }
    cout << res + 1 << endl;
}

void process2(int tt) {
    if(tt>tinh(n,m) || tt<=0) {
        cout << "Incorrect data" << endl;
        return;
    }
    bool b[26];
    char res[30];
    res[m] = 0;
    memset( b, 0, sizeof(b));
    for(int i=0;i<m;++i) {
        for(int c=0;c<n;++c) if(!b[c]) {
            if(tt<=tinh(n-i-1,m-i-1)) {
                res[i] = c + 'a';
                b[c] = true;
                break;
            }
            else tt -= tinh(n-i-1,m-i-1);
        }
    }
    puts(res);
}

int main() {
    int st, t;
    scanf("%d", &st);
    for(t=1;t<=st;++t) {
        scanf("%d%d", &n, &m);
        char buf[100];
        gets(buf);
        gets(buf);
        if(buf[0]=='P') {
            process( buf + 2 );
        }
        else {
            int tt;
            sscanf(buf+2, "%d", &tt);
            process2(tt);
        }
    }
    return 0;
}