From 92df810943b637bd612abbf1cea5291c3249e326 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Anders=20Engl=C3=B6f=20Ytterstr=C3=B6m?= <yttan@fastmail.se>
Date: Sun, 30 Nov 2025 18:48:52 +0100
Subject: [PATCH] Solve 2022 day 12 pt 1-2

BFS, baby.

2 things got me.

 * S position was not (0,0) in the puzzle input. Such embarrasment to
   loose time over something so stupid.
 * I asumed the elevation was fixed to to increase AND DECREASE by 1.

From the problem description:

> To avoid needing to get out your climbing gear, the elevation of the
> destination square can be at most one higher than the elevation of
> your current square; that is, if your current elevation is m, you
> could step to elevation n, but not to elevation o. _(This also means
> that the elevation of the destination square can be much lower than
> the elevation of your current square.)_

This means elevation only can _increase_ by one,
but _decrease_ with more.

So my wrong code:

0 <= abs(n - e) <= 1

got fixed with:

n - e <= 1

For pt 2, I reused the loop to find S to collect all "a" positions,
and looped them as starting points. Execution time is not the best,
but it works.
---
 2022-python/output/__init__.py |  6 ++++
 2022-python/output/day_12.py   | 58 ++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 2022-python/output/day_12.py

diff --git a/2022-python/output/__init__.py b/2022-python/output/__init__.py
index ba3186c..809c3f5 100644
--- a/2022-python/output/__init__.py
+++ b/2022-python/output/__init__.py
@@ -78,6 +78,12 @@ def vdbg(seen, h, w):
         print("".join(["#" if (r, c) in seen else " " for c in range(w)]))
 
 
+def vvdbg(seen, h, w):
+    """Print-debug visited positions of a matrix, with values"""
+    for r in range(h):
+        print("".join([seen[(r, c)] if (r, c) in seen else "." for c in range(w)]))
+
+
 def cw(y, x):
     """Flip a (y, x) direction counterwise: U->R, R->D, D->L, L->U.
 
diff --git a/2022-python/output/day_12.py b/2022-python/output/day_12.py
new file mode 100644
index 0000000..cb6d27a
--- /dev/null
+++ b/2022-python/output/day_12.py
@@ -0,0 +1,58 @@
+import re
+from collections import deque, Counter, defaultdict
+from heapq import heappop, heappush
+from itertools import compress, combinations, chain, permutations
+
+from output import matrix, D, DDa, vvdbg, DD, ADJ, ints, mhd, mdbg, vdbg, cw, ccw, bk
+
+
+def solve(data):
+    M, H, W = matrix(data)
+    E = S = None
+    p1 = p2 = H * W
+    SP = []
+    for rr in range(H):
+        for cc in range(W):
+            if M[rr][cc] == "E":
+                E = (rr, cc)
+            if M[rr][cc] == "S":
+                S = (rr, cc)
+                SP.append((rr, cc))
+            if M[rr][cc] == "a":
+                SP.append((rr, cc))
+    M = [list(row) for row in M]
+    for rc, v in [(S, "a"), (E, "z")]:
+        r, c = rc
+        M[r][c] = v
+    for sp in SP:
+        Q = [(sp, ord("a"), 0)]
+        seen = set()
+        while Q:
+            yx, e, s = Q.pop(0)
+            if yx in seen:
+                continue
+            seen.add(yx)
+            if yx == E:
+                if sp == S:
+                    p1 = s
+                p2 = min(p2, s)
+            y, x = yx
+            for dy, dx in D:
+                if 0 <= y + dy < H and 0 <= x + dx < W:
+                    n = ord(M[y + dy][x + dx])
+                    if n - e <= 1:
+                        Q.append(((y + dy, x + dx), n, s + 1))
+    return p1, p2
+
+
+if __name__ == "__main__":
+    with open("./input/12.txt", "r") as f:
+        inp = f.read().strip()
+
+    p1, p2 = solve(inp)
+
+    print(p1)
+    print(p2)
+
+    assert p1 == 517
+    assert p2 == 512