Data commit

Task/Descending-primes/Delphi/descending-primes.delphi

@@ -0,0 +1,63 @@
+type TProgress = procedure(Percent: integer);
+
+
+function IsPrime(N: integer): boolean;
+{Optimised prime test - about 40% faster than the naive approach}
+var I,Stop: integer;
+begin
+if (N = 2) or (N=3) then Result:=true
+else if (n <= 1) or ((n mod 2) = 0) or ((n mod 3) = 0) then Result:= false
+else
+	begin
+	I:=5;
+	Stop:=Trunc(sqrt(N));
+	Result:=False;
+	while I<=Stop do
+		begin
+		if ((N mod I) = 0) or ((N mod (i + 2)) = 0) then exit;
+		Inc(I,6);
+		end;
+	Result:=True;
+	end;
+end;
+
+function IsDescending(N: integer): boolean;
+{Determine if each digit is less than previous, left to right}
+var S: string;
+var I: integer;
+begin
+Result:=False;
+S:=IntToStr(N);
+for I:=1 to Length(S)-1 do
+ if S[I]<=S[I+1] then exit;
+Result:=True;
+end;
+
+
+procedure ShowDescendingPrimes(Memo: TMemo; Prog: TProgress);
+{Write Descending primes up to 123,456,789 }
+{The Optional progress }
+var I,Cnt: integer;
+var S: string;
+const Max = 123456789;
+begin
+if Assigned(Prog) then Prog(0);
+S:='';
+Cnt:=0;
+for I:=2 to Max do
+	begin
+	if ((I mod 1000000)=0) and Assigned(Prog) then Prog(Trunc(100*(I/Max)));
+	if IsDescending(I) and IsPrime(I) then
+		begin
+		S:=S+Format('%12.0n', [I*1.0]);
+		Inc(Cnt);
+		if (Cnt mod 8)=0 then
+			begin
+			Memo.Lines.Add(S);
+			S:='';
+			end;
+		end;
+	end;
+if S<>'' then Memo.Lines.Add(S);
+Memo.Lines.Add('Descending Primes Found: '+IntToStr(Cnt));
+end;