On 9/20/13, Reinier Olislagers <reinierolislag...@gmail.com> wrote:
> The question however becomes "what is the
> algorithm for deciding invalid characters" which IMO will become a mess
> very quickly. Much better to just consider the entire input as invalid.
>
Here's my implementation:
program test;
{$mode objfpc}
{$H+}
uses
SysUtils, StrUtils;
function TryRomanToInt(S: String; out N: Integer): Boolean;
var
i, Len: Integer;
Terminated: Boolean;
begin
Result := (False);
S := UpperCase(S); //don't use AnsiUpperCase please
Len := Length(S);
if (Len = 0) then Exit;
i := 1;
N := 0;
Terminated := False;
//leading M's
while (i <= Len) and (S[i] = 'M') do
begin
//writeln('TryRomanToInt: Found 1000');
Inc(i);
N := N + 1000;
end;
//then CM or or CD or D or (C, CC, CCC, CCCC)
if (i <= Len) and (S[i] = 'D') then
begin
//writeln('TryRomanToInt: Found 500');
Inc(i);
N := N + 500;
end
else if (i + 1 <= Len) and (S[i] = 'C') then
begin
if (S[i+1] = 'M') then
begin
//writeln('TryRomanToInt: Found 900');
Inc(i,2);
N := N + 900;
end
else if (S[i+1] = 'D') then
begin
//writeln('TryRomanToInt: Found 400');
Inc(i,2);
N := N + 400;
end;
end ;
//next max 4 C's
if (i <= Len) and (S[i] = 'C') then
begin
//find max 4 C's
//writeln('TryRomanToInt: Found 100');
Inc(i);
N := N + 100;
if (i <= Len) and (S[i] = 'C') then
begin
//writeln('TryRomanToInt: Found 100');
Inc(i);
N := N + 100;
end;
if (i <= Len) and (S[i] = 'C') then
begin
//writeln('TryRomanToInt: Found 100');
Inc(i);
N := N + 100;
end;
if (i <= Len) and (S[i] = 'C') then
begin
//writeln('TryRomanToInt: Found 100');
Inc(i);
N := N + 100;
end;
end;
//then XC or XL
if (i + 1 <= Len) and (S[i] = 'X') then
begin
if (S[i+1] = 'C') then
begin
//writeln('TryRomanToInt: Found 90');
Inc(i,2);
N := N + 90;
end
else if (S[i+1] = 'L') then
begin
//writeln('TryRomanToInt: Found 40');
Inc(i,2);
N := N + 40;
end;
end;
//then L
if (i <= Len) and (S[i] = 'L') then
begin
//writeln('TryRomanToInt: Found 50');
Inc(i);
N := N + 50;
end;
//then (X, xx, xxx, xxxx)
if (i <= Len) and (S[i] = 'X') then
begin
//find max 4 X's
//writeln('TryRomanToInt: Found 10');
Inc(i);
N := N + 10;
if (i <= Len) and (S[i] = 'X') then
begin
//writeln('TryRomanToInt: Found 10');
Inc(i);
N := N + 10;
end;
if (i <= Len) and (S[i] = 'X') then
begin
//writeln('TryRomanToInt: Found 10');
Inc(i);
N := N + 10;
end;
if (i <= Len) and (S[i] = 'X') then
begin
//writeln('TryRomanToInt: Found 10');
Inc(i);
N := N + 10;
end;
end;
//then IX or IV
if (i + 1 <= Len) and (S[i] = 'I') then
begin
if (S[i+1] = 'X') then
begin
Terminated := (True);
//writeln('TryRomanToInt: Found 9');
Inc(i,2);
N := N + 9;
end
else if (S[i+1] = 'V') then
begin
Terminated := (True);
//writeln('TryRomanToInt: Found 4');
Inc(i,2);
N := N + 4;
end;
end;
//then V
if (not Terminated) and (i <= Len) and (S[i] = 'V') then
begin
//writeln('TryRomanToInt: Found 5');
Inc(i);
N := N + 5;
end;
//then I
if (not Terminated) and (i <= Len) and (S[i] = 'I') then
begin
Terminated := (True);
//writeln('TryRomanToInt: Found 1');
Inc(i);
N := N + 1;
//Find max 3 closing I's
if (i <= Len) and (S[i] = 'I') then
begin
//writeln('TryRomanToInt: Found 1');
Inc(i);
N := N + 1;
end;
if (i <= Len) and (S[i] = 'I') then
begin
//writeln('TryRomanToInt: Found 1');
Inc(i);
N := N + 1;
end;
if (i <= Len) and (S[i] = 'I') then
begin
//writeln('TryRomanToInt: Found 1');
Inc(i);
N := N + 1;
end;
end;
//writeln('TryRomanToInt: Len = ',Len,' i = ',i);
Result := (i > Len);
//if Result then writeln('TryRomanToInt: N = ',N);
end;
var
S: String;
N1, N2: Integer;
B: Boolean;
begin
repeat
write('Enter Roman numeral: ');
readln(S);
B := TryRomanToInt(S, N1);
if B then
write('TryRomanToInt(''',S,''') -> ',N1)
else
write('TryRomanToInt(''',S,''') FAIL');
writeln;
N2 := StrUtils.RomanToInt(S);
writeln('StrUtils.RomanToInt(''',S,''') = ',N2);
if B and (N1 <> N2) then writeln('StrUtils.RomanToInt <> TryRomanToInt');
writeln;
until S = '';
end.
Bart
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