Day 3: Mull It Over
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Sorry for the delay posting this one, Ategon seemed to have it covered, so I forgot :D I will do better.
Haskell
Oof, a parsing problem :/ This is some nasty-ass code. step is almost the State monad written out explicitly.
Solution
import Control.Monad
import Data.Either
import Data.List
import Text.Parsec
data Ins = Mul !Int !Int | Do | Dont
readInput :: String -> [Ins]
readInput = fromRight undefined . parse input ""
where
input = many ins <* many anyChar
ins =
choice . map try $
[ Mul <$> (string "mul(" *> arg) <*> (char ',' *> arg) <* char ')',
Do <$ string "do()",
Dont <$ string "don't()",
anyChar *> ins
]
arg = do
s <- many1 digit
guard $ length s <= 3
return $ read s
run f = snd . foldl' step (True, 0)
where
step (e, a) i =
case i of
Mul x y -> (e, if f e then a + x * y else a)
Do -> (True, a)
Dont -> (False, a)
main = do
input <- readInput <$> readFile "input03"
print $ run (const True) input
print $ run id input
Love to see you chewing through this parsing problem in Haskell, I didn’t dare use Parsec because I wasn’t confident enough.
Why did you decide to have a strict definition of Mul !Int !Int?
My guess is because a linter and/or HLS was suggesting it. I know HLS used to suggest making your fields strict in almost all cases. In this case I have a hunch that it slightly cuts down on memory usage because we use almost all Muls either way. So it does not need to keep the string it is parsed from in memory as part of the thunk.
But it probably makes a small/negligible difference here.
Nim
From a first glance it was obviously a regex problem.
I’m using tinyre here instead of stdlib re library just because I’m more familiar with it.
import pkg/tinyre
proc solve(input: string): AOCSolution[int, int] =
var allow = true
for match in input.match(reG"mul\(\d+,\d+\)|do\(\)|don't\(\)"):
if match == "do()": allow = true
elif match == "don't()": allow = false
else:
let pair = match[4..^2].split(',')
let mult = pair[0].parseInt * pair[1].parseInt
result.part1 += mult
if allow: result.part2 += mult
C
Yay parsers! I’ve gotten quite comfortable writing these with C. Using out pointers arguments for the cursor that are only updated if the match is successful makes for easy bookkeeping.
Code
#include "common.h"
static int
parse_exact(const char **stringp, const char *expect)
{
const char *s = *stringp;
int i;
for (i=0; s[i] && expect[i] && s[i] == expect[i]; i++)
;
if (expect[i])
return 0;
*stringp = &s[i];
return 1;
}
static int
parse_int(const char **stringp, int *outp)
{
char *end;
int val;
val = (int)strtol(*stringp, &end, 10);
if (end == *stringp)
return 0;
*stringp = end;
if (outp) *outp = val;
return 1;
}
static int
parse_mul(const char **stringp, int *ap, int *bp)
{
const char *cur = *stringp;
int a,b;
if (!parse_exact(&cur, "mul(") ||
!parse_int(&cur, &a) ||
!parse_exact(&cur, ",") ||
!parse_int(&cur, &b) ||
!parse_exact(&cur, ")"))
return 0;
*stringp = cur;
if (ap) *ap = a;
if (bp) *bp = b;
return 1;
}
int
main(int argc, char **argv)
{
static char buf[32*1024];
const char *cur;
size_t nr;
int p1=0,p2=0, a,b, dont=0;
if (argc > 1)
DISCARD(freopen(argv[1], "r", stdin));
nr = fread(buf, 1, sizeof(buf), stdin);
assert(!ferror(stdin));
assert(nr != sizeof(buf));
buf[nr] = '\0';
for (cur = buf; *cur; )
if (parse_exact(&cur, "do()"))
dont = 0;
else if (parse_exact(&cur, "don't()"))
dont = 1;
else if (parse_mul(&cur, &a, &b)) {
p1 += a * b;
if (!dont) p2 += a * b;
} else
cur++;
printf("03: %d %d\n", p1, p2);
}
Got the code a little shorter:
Code
#include "common.h"
static int
parse_mul(const char **stringp, int *ap, int *bp)
{
const char *cur = *stringp, *end;
if (strncmp(cur, "mul(", 4)) { return 0; } cur += 4;
*ap = (int)strtol(cur, (char **)&end, 10);
if (end == cur) { return 0; } cur = end;
if (*cur != ',') { return 0; } cur += 1;
*bp = (int)strtol(cur, (char **)&end, 10);
if (end == cur) { return 0; } cur = end;
if (*cur != ')') { return 0; } cur += 1;
*stringp = cur;
return 1;
}
int
main(int argc, char **argv)
{
static char buf[32*1024];
const char *p;
size_t nr;
int p1=0,p2=0, a,b, dont=0;
if (argc > 1)
DISCARD(freopen(argv[1], "r", stdin));
nr = fread(buf, 1, sizeof(buf), stdin);
assert(!ferror(stdin));
assert(nr != sizeof(buf));
buf[nr] = '\0';
for (p = buf; *p; )
if (parse_mul(&p, &a, &b)) { p1 += a*b; p2 += a*b*!dont; }
else if (!strncmp(p, "do()", 4)) { dont = 0; p += 4; }
else if (!strncmp(p, "don't()", 7)) { dont = 1; p += 7; }
else p++;
printf("03: %d %d\n", p1, p2);
}
Uiua
Uses experimental feature of fold to track the running state of do/don’t.
[edit] Slightly re-written to make it less painful :-) Try it online!
# Experimental!
DataP₁ ← $ xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))
DataP₂ ← $ xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))
GetMul ← $ mul\((\d{1,3}),(\d{1,3})\)
GetMulDoDont ← $ mul\(\d{1,3},\d{1,3}\)|do\(\)|don\'t\(\)
&p/+≡(/×≡⋕↘1)regexGetMul DataP₁ # Part 1
# Build an accumulator to track running state of do/don't
Filter ← ↘1⊂:∧(⍣(0 °"don"|1 °"do("|.◌)) :1≡(↙3°□)
≡⊢ regex GetMulDoDont DataP₂
▽⊸≡◇(≍"mul"↙3)▽⊸Filter # Apply Filter, remove the spare 'do's
&p/+≡◇(/×≡◇⋕↘1⊢regexGetMul) # Get the digits and multiply, sum.
