advent of code day 10

advent of code day 10

[Stephen Leake]

This was a more interesting puzzle. It is almost "sort, find consecutive
skips, multiply by n choose k", but not quite.

I cheated; the final total is larger than 64 bits, so I just printed out
the factors and used Emacs built-in bignums to compute it. I assume
there is an Ada bignums package out there, and the compiler has one that
full Ada 2020 will expose, but I'm trying to catch up, so did not look.

-- 
-- Stephe

Re: advent of code day 10

[Jared Summers]

On Thursday, December 10, 2020 at 8:39:36 PM UTC-7, Stephen Leake wrote:
> I cheated; the final total is larger than 64 bits, so I just printed out 
> the factors and used Emacs built-in bignums to compute it. I assume 
> there is an Ada bignums package out there, and the compiler has one that 
> full Ada 2020 will expose, but I'm trying to catch up, so did not look. 

My answer was able to fit in a Long_Long_Integer on my machine. But, due to a bug, I did play with the Big_Integers package. It worked well, and I'd recommend taking a look at it for upcoming problems. Based on past years it'll be useful to have on hand.

--
Jared

Re: advent of code day 10

[Stephen Leake]

Jared Summers <jtsummers@gmail.com> writes:

> On Thursday, December 10, 2020 at 8:39:36 PM UTC-7, Stephen Leake wrote:
>> I cheated; the final total is larger than 64 bits, so I just printed out 
>> the factors and used Emacs built-in bignums to compute it. I assume 
>> there is an Ada bignums package out there, and the compiler has one that 
>> full Ada 2020 will expose, but I'm trying to catch up, so did not look. 
>
> My answer was able to fit in a Long_Long_Integer on my machine. But,
> due to a bug, I did play with the Big_Integers package. It worked
> well, and I'd recommend taking a look at it for upcoming problems.

Yes; GNAT Community 2020 with -gnat2020 and -gnatX supports
Ada.Numerics.Big_Integer. I updated my solution to use that.

-- 
-- Stephe

Re: advent of code day 10

[gautier...@hotmail.com]

On Friday, December 11, 2020 at 4:39:36 AM UTC+1, Stephen Leake wrote:
> I cheated; the final total is larger than 64 bits, so I just printed out 
> the factors and used Emacs built-in bignums to compute it. I assume 
> there is an Ada bignums package out there, and the compiler has one that 
> full Ada 2020 will expose, but I'm trying to catch up, so did not look. 

It's surprising how different in scale the answers are, depending on the input data.
Mine was "only" around 37 trillion.

Re: advent of code day 10

[gautier...@hotmail.com]

On Friday, December 11, 2020 at 4:39:36 AM UTC+1, Stephen Leake wrote:
> the final total is larger than 64 bits
The total for your data is 3022415986688, it holds in 42 bits...

Re: advent of code day 10

[Stephen Leake]

"gautier...@hotmail.com" <gautier_niouzes@hotmail.com> writes:

> On Friday, December 11, 2020 at 4:39:36 AM UTC+1, Stephen Leake wrote:
>> the final total is larger than 64 bits
> The total for your data is 3022415986688, it holds in 42 bits...

hmm. I got constraint error when I used Long_Integer; maybe that's not
64 bits? Using Ada.Big_Numbers.Big_Integers was a good exercise anyway.

-- 
-- Stephe

Re: advent of code day 10

[Jeffrey R. Carter]

On 12/12/20 9:17 PM, Stephen Leake wrote:
> "gautier...@hotmail.com" <gautier_niouzes@hotmail.com> writes:
> 
>> On Friday, December 11, 2020 at 4:39:36 AM UTC+1, Stephen Leake wrote:
>>> the final total is larger than 64 bits
>> The total for your data is 3022415986688, it holds in 42 bits...
> 
> hmm. I got constraint error when I used Long_Integer; maybe that's not
> 64 bits? Using Ada.Big_Numbers.Big_Integers was a good exercise anyway.

That sounds like C thinking. If you need 64 bits, say so, don't hope that 
optional language-defined types will be big enough.

type S is range -(2 ** 63) + 1 .. 2 ** 63 - 1;
type U is mod 2 ** 64;

I used

type U is mod System.Max_Binary_Modulus;

-- 
Jeff Carter
"Frankie Wolf, wanted by Federal authorities for
dancing with a mailman."
Take the Money and Run
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