Advent of Code 2024 Day 4

Placed 723/215.
Problem: adventofcode.c...
Solution: github.com/jon...
I had two bugs in part 1; I forgot about up-right/down-left and I had an off-by-one in the "in-bounds" condition for up-right/down-left.
Not sure what I should've done to go faster here. Probably "don't have bugs"?

[@рнт]

Interesting! What I did for part 2 is to iterate through all 'A's (accounting the borders!) and check if it's X-MAS by checking if sums of corner ASCII values are equal to 'M'+'S'. I like this solution since it ignores the order of corner letters :)

[@antoineleduc7611]

:O very nice

[@siddmittal6907]

just wanted to say that is an absolutely genius solution. nice work!

[@ungerfall]

For part 1 I used directions approach. Starting from 'X' outward in all directions

[@svinther]

Good for your approach that the searchstring was quite short :-) . I used a dfs like approach, starting with all the positions having the first character of the searchstring

[@reik2006]

Did you by any chance also make the mistake of looking in all directions for next letter in the search string without considering the direction you came from? :-)

[@chandra_83]

This solution is fantastic.

[@fredoverflow]

Could you configure OBS not to record those annoying Windows sounds?

[@rastislavsvoboda4363]

I wish you better luck for next days...

[@harisimer]

off by 1 errors never getting tired of reappearing.

[@ahxxm]

I might save some time with try except to replace r2+r

[@jonathanpaulson5053]

It’s a good idea but I don’t think it works with negative indices? (They are valid and wrap-around to the end)

[@ahxxm]

@@jonathanpaulson5053 oh! yeah, convenient python feature

[@rastislavsvoboda4363]

for part2:
def get_X_directions(r,c):
return [[(r+0,c+0),(r+0,c+2),(r+1,c+1),(r+2,c+0),(r+2,c+2)]]
with something like this:
...
res = 0
for r in range(R):
for c in range(C):
dirs = get_X_directions(r,c)
for word in ["MSAMS", "MMASS", "SMASM", "SSAMM"]:
n = check(dirs, word, D)
res += n
return res
maybe the optimal would be
for r in range(1, R-1):
for c in range(1, C-1):
if D[r][c] == "A":
dirs = [[(r-1,c-1),(r-1,c+1),(r+1,c+1),(r+1,c-1)]]
for word in ["MSSM", "MMSS", "SMMS", "SSMM"]:
res += check(dirs, word, D)

[@prateeksaraswat1]

Loved it!

[@rastislavsvoboda4363]

first I used
def check1(r, c, D):
RR = len(D)
CC = len(D[0])
res = 0
if c+3 in range(CC) and D[r][c] == "X" and D[r][c+1] == "M" and D[r][c+2] == "A" and D[r][c+3] == "S":
res += 1
if c-3 in range(CC) and D[r][c] == "X" and D[r][c-1] == "M" and D[r][c-2] == "A" and D[r][c-3] == "S":
res += 1
if r+3 in range(RR) and D[r][c] == "X" and D[r+1][c] == "M" and D[r+2][c] == "A" and D[r+3][c] == "S":
res += 1
if r-3 in range(RR) and D[r][c] == "X" and D[r-1][c] == "M" and D[r-2][c] == "A" and D[r-3][c] == "S":
res += 1
if r+3 in range(RR) and c+3 in range(CC) and D[r][c] == "X" and D[r+1][c+1] == "M" and D[r+2][c+2] == "A" and D[r+3][c+3] == "S":
res += 1
if r-3 in range(RR) and c-3 in range(CC) and D[r][c] == "X" and D[r-1][c-1] == "M" and D[r-2][c-2] == "A" and D[r-3][c-3] == "S":
res += 1
if r+3 in range(RR) and c-3 in range(CC) and D[r][c] == "X" and D[r+1][c-1] == "M" and D[r+2][c-2] == "A" and D[r+3][c-3] == "S":
res += 1
if r-3 in range(RR) and c+3 in range(CC) and D[r][c] == "X" and D[r-1][c+1] == "M" and D[r-2][c+2] == "A" and D[r-3][c+3] == "S":
res += 1
return res
later refactored just for fun to two methods, first to get coordinates, second check if correct char is at appropriate location
def get_8_directions(r, c, word):
res = []
L = len(word)
for dr in [-1, 0, 1]:
for dc in [-1, 0, 1]:
if (dr,dc) != (0,0):
res.append([(r + i * dr, c + i * dc) for i in range(L)])
return res
def check(dirs, word, M):
res = 0
R = len(M)
C = len(M[0])
for lst in dirs:
if all([r in range(R) and c in range(C) and M[r][c] == word[i] for i, (r, c) in enumerate(lst)]):
res += 1
return res