commit eb233235c876600bafa39a538d18ce11cfc72b39
parent 61718ca8b469ebad7ed59da0ed3c167046cd8e57
Author: Sebastiano Tronto <sebastiano@tronto.net>
Date: Sun, 7 Dec 2025 09:14:27 +0100
Clean up and alternative solution to day 7
Diffstat:
4 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/2025/07/a.py b/2025/07/a.py
@@ -2,9 +2,9 @@ import fileinput
with fileinput.input() as lines:
rows = [line[:-1] for line in lines]
- pos = [rows[0].find('S')]
s = 0
+pos = [rows[0].find('S')]
for row in rows[1:]:
newpos = set()
for p in pos:
diff --git a/2025/07/b.py b/2025/07/b.py
@@ -2,8 +2,8 @@ import fileinput
with fileinput.input() as lines:
rows = [line[:-1] for line in lines]
- pos = {rows[0].find('S'): 1}
+pos = {rows[0].find('S'): 1}
for row in rows[1:]:
newpos = {}
for p, w in pos.items():
diff --git a/2025/07/b2.py b/2025/07/b2.py
@@ -0,0 +1,17 @@
+import fileinput
+
+with fileinput.input() as lines:
+ rows = [line[:-1] for line in lines]
+
+t = [1 if x == 'S' else 0 for x in rows[0]]
+for row in rows[1:]:
+ next = [0] * len(row)
+ for i in range(len(row)):
+ if row[i] == '^':
+ next[i-1] += t[i]
+ next[i+1] += t[i]
+ else:
+ next[i] += t[i]
+ t = next
+
+print(sum(t))
diff --git a/2025/README.md b/2025/README.md
@@ -96,3 +96,7 @@ changed to a map where the keys are the positions and the values are the
number of multiverses where a tachyon is in that position. To update
this value for the current row, I sum the values of all tachyons that
end there from the previous row (that can be one or two tachyons).
+
+I added a second solution for part 2 that does not use a map, but only
+lists. This could be seen as a dynamic programming problem where the
+iterative implementation is more intuitive than the recursive one.
