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  1. {$mode objfpc}
  2. uses math;
  3. const
  4.                 finp            =               '';
  5.                 fout            =               '';
  6.                 modulo          =               trunc(1e9+7);
  7.                 maxn            =               2000;
  8. var
  9.                 fi,fo           :               text;
  10.                 n,h             :               integer;
  11.                 f               :               array[1..maxn,0..maxn] of int64;
  12.                 a               :               array[1..maxn] of integer;
  13. procedure openfile;
  14. begin
  15.         assign(fi,finp);reset(fi);
  16.         assign(fo,fout);rewrite(fo);
  17. end;
  18. procedure closefile;
  19. begin
  20.         close(fi);close(fo);
  21. end;
  22. procedure enter;
  23. var
  24.         i               :               integer;
  25. begin
  26.         readln(fi,n,h);
  27.         for i:=1 to n do
  28.                 read(fi,a[i]);
  29. end;
  30. procedure add(var a:int64;b:int64);
  31. begin
  32.         a:=(a+b) mod modulo;
  33. end;
  34. procedure process;
  35. var
  36.         i,j             :               integer;
  37. begin
  38.         //Tai 1 [] hoac do no thing
  39.         f[1][0]:=ord((a[i]=h) or (a[i]+1=h));
  40.         //Tai 1 [
  41.         f[1][1]:=ord(a[i]+1=h);
  42.         for i:=2 to n do
  43.         for j:=max(h-a[i]-1,0) to min(h-a[i],i) do
  44.         begin
  45.                 //
  46.                 if j+a[i]=h then
  47.                 begin
  48.                         //Tai i [
  49.                         if j>0 then
  50.                                 add(f[i,j],f[i-1,j-1]);
  51.                         //Do no thing
  52.                         add(f[i,j],f[i-1,j]);
  53.                 end
  54.                 else
  55.                 if j+a[i]+1=h then
  56.                 begin
  57.                         //Tai i ]
  58.                         add(f[i,j],f[i-1,j+1]*(j+1));
  59.                         //Tai i []
  60.                         add(f[i,j],f[i-1,j]);
  61.                         //Tai i ][
  62.                         add(f[i,j],f[i-1,j]*j);
  63.                 end;
  64.         end;
  65.         writeln(fo,f[n,0]);
  66. end;
  67. begin
  68.         openfile;
  69.         enter;
  70.         process;
  71.         closefile;
  72. end.
Success #stdin #stdout 0s 31680KB
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https://ideone.com/6lt8wR
language:
Pascal (fpc 3.0.4)
created:
9 years ago
visibility:
public

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