Add day 04, 2025

Author: snhansen

2025/day04/solution.py

@@ -0,0 +1,43 @@
+with open("input") as f:
+    inp = f.read().strip().split("\n")
+
+grid = {x + y*1j: c for y, line in enumerate(inp) for x, c in enumerate(line)}
+
+
+def accessible_rolls(grid):
+    dirs = [1, -1, 1j, -1j, 1+1j, 1-1j, -1+1j, -1-1j]
+    res = []
+    for p in grid:
+        if grid[p] == ".":
+            continue
+        rolls = 0
+        for dp in dirs:
+            if p + dp in grid and grid[p + dp] == "@":
+                rolls += 1
+        if rolls < 4:
+            res.append(p)
+
+    return res
+
+
+# Part 1
+print(len(accessible_rolls(grid)))
+
+
+# Part 2
+def update_grid(grid):
+    ps = accessible_rolls(grid)
+    for p in ps:
+        grid[p] = "."
+
+    return len(ps), grid
+
+
+ans = 0
+while True:
+    n, grid = update_grid(grid)
+    ans += n
+    if n == 0:
+        break
+
+print(ans)