107 lines
2.1 KiB
Text
107 lines
2.1 KiB
Text
MODULE Emirp;
|
|
FROM Conversions IMPORT StrToLong;
|
|
FROM FormatString IMPORT FormatString;
|
|
FROM LongMath IMPORT sqrt;
|
|
FROM Terminal IMPORT WriteString,WriteLn,ReadChar;
|
|
|
|
PROCEDURE IsPrime(x : LONGINT) : BOOLEAN;
|
|
VAR
|
|
i : LONGINT;
|
|
u : LONGREAL;
|
|
v : LONGINT;
|
|
BEGIN
|
|
IF x<2 THEN RETURN FALSE END;
|
|
IF x=2 THEN RETURN TRUE END;
|
|
IF x MOD 2 = 0 THEN RETURN FALSE END;
|
|
|
|
u := sqrt(FLOAT(x));
|
|
v := TRUNC(u);
|
|
|
|
FOR i:=3 TO v BY 2 DO
|
|
IF x MOD i = 0 THEN RETURN FALSE END
|
|
END;
|
|
|
|
RETURN TRUE
|
|
END IsPrime;
|
|
|
|
PROCEDURE IsEmirp(x : LONGINT) : BOOLEAN;
|
|
VAR
|
|
buf,rev : ARRAY[0..9] OF CHAR;
|
|
i,j : INTEGER;
|
|
y : LONGINT;
|
|
BEGIN
|
|
(* Terminate early if the number is even *)
|
|
IF x MOD 2 = 0 THEN RETURN FALSE END;
|
|
|
|
(* First convert the input to a string *)
|
|
FormatString("%l", buf, x);
|
|
|
|
(* Create a copy of the string revered *)
|
|
j := 0;
|
|
WHILE buf[j] # 0C DO INC(j) END;
|
|
DEC(j);
|
|
i := 0;
|
|
WHILE buf[i] # 0C DO
|
|
rev[i] := buf[j];
|
|
INC(i);
|
|
DEC(j)
|
|
END;
|
|
rev[i] := 0C;
|
|
|
|
(* Convert the reversed copy to a number *)
|
|
StrToLong(rev,y);
|
|
|
|
(* Terminate early if the number is even *)
|
|
IF y MOD 2 = 0 THEN RETURN FALSE END;
|
|
|
|
(* Discard palindromes *)
|
|
IF x=y THEN RETURN FALSE END;
|
|
|
|
RETURN IsPrime(x) AND IsPrime(y)
|
|
END IsEmirp;
|
|
|
|
VAR
|
|
buf : ARRAY[0..63] OF CHAR;
|
|
x,count : LONGINT;
|
|
BEGIN
|
|
count := 0;
|
|
x := 1;
|
|
|
|
WriteString("First 20 emirps:");
|
|
WriteLn;
|
|
WHILE count<20 DO
|
|
IF IsEmirp(x) THEN
|
|
INC(count);
|
|
FormatString("%l ", buf, x);
|
|
WriteString(buf)
|
|
END;
|
|
INC(x)
|
|
END;
|
|
WriteLn;
|
|
|
|
WriteString("Emirps between 7700 and 8000:");
|
|
WriteLn;
|
|
FOR x:=7700 TO 8000 DO
|
|
IF IsEmirp(x) THEN
|
|
FormatString("%l ", buf, x);
|
|
WriteString(buf)
|
|
END
|
|
END;
|
|
WriteLn;
|
|
|
|
WriteString("10,000th emirp:");
|
|
WriteLn;
|
|
count := 0;
|
|
x := 1;
|
|
WHILE count<10000 DO
|
|
IF IsEmirp(x) THEN
|
|
INC(count);
|
|
END;
|
|
INC(x)
|
|
END;
|
|
FormatString("%l ", buf, x-1);
|
|
WriteString(buf);
|
|
WriteLn;
|
|
|
|
ReadChar
|
|
END Emirp.
|