Day 11, 12, 13.

d12.py

@@ -0,0 +1,120 @@
+import lib
+
+EXAMPLE = """
+Sabqponm
+abcryxxl
+accszExk
+acctuvwj
+abdefghi
+"""
+
+def neighbors_4(row, col, rows, cols):
+    n = []
+    for r, c in [(1, 0), (-1, 0), (0, 1), (0, -1)]:
+        new_row, new_col = row + r, col + c
+        if new_row >= 0 and new_row < rows and new_col >= 0 and new_col < cols:
+            n.append((new_row, new_col))
+    return n
+
+def solve(lines: list[str]):
+    start = (0, 0)
+    end = (0, 0)
+    rows = len(lines)
+    cols = len(lines[0])
+    heights = []
+    dists = []
+    for (row, line) in enumerate(lines):
+        heights.append([])
+        dists.append([])
+        for (col, c) in enumerate(line):
+            if c == 'S':
+                start = (row, col)
+                heights[row].append(0)
+                dists[row].append(0)
+            elif c == 'E':
+                end = (row, col)
+                heights[row].append(26)
+                dists[row].append(2**16)
+            else:
+                heights[row].append(ord(lines[row][col]) - ord('a'))
+                dists[row].append(2**16)
+
+    active_fields = [start]
+    while active_fields:
+        row, col = active_fields.pop()
+        current_dist = dists[row][col]
+        current_height = heights[row][col]
+        for row, col in neighbors_4(row, col, rows, cols):
+            pot_height = heights[row][col]
+            if current_height < pot_height - 1:
+                continue
+            if current_dist + 1 < dists[row][col]:
+                dists[row][col] = current_dist + 1
+                active_fields.append((row, col))
+
+    # for row in dists:
+    #     print(row)
+
+    # 34:00
+    return dists[end[0]][end[1]]
+
+def solve2(lines: list[str]):
+    starts = []
+    all_dists =[]
+    for (row, line) in enumerate(lines):
+        for (col, c) in enumerate(line):
+            if c == 'S' or c == 'a':
+                starts.append((row, col))
+
+    for start in starts:
+        end = (0, 0)
+        rows = len(lines)
+        cols = len(lines[0])
+        heights = []
+        dists = []
+        for (row, line) in enumerate(lines):
+            heights.append([])
+            dists.append([])
+            for (col, c) in enumerate(line):
+                if row == start[0] and col == start[1]:
+                    heights[row].append(0)
+                    dists[row].append(0)
+                elif c == 'E':
+                    end = (row, col)
+                    heights[row].append(26)
+                    dists[row].append(2**16)
+                else:
+                    heights[row].append(ord(lines[row][col]) - ord('a'))
+                    dists[row].append(2**16)
+
+        active_fields = [start]
+        while active_fields:
+            row, col = active_fields.pop()
+            current_dist = dists[row][col]
+            current_height = heights[row][col]
+            for row, col in neighbors_4(row, col, rows, cols):
+                pot_height = heights[row][col]
+                if current_height < pot_height - 1:
+                    continue
+                if current_dist + 1 < dists[row][col]:
+                    dists[row][col] = current_dist + 1
+                    active_fields.append((row, col))
+        all_dists.append(dists[end[0]][end[1]])
+    # 39:45
+    return min(all_dists)
+
+def main():
+    lines = lib.str_to_lines_no_empty(EXAMPLE)
+    print("Example  1:", solve(lines))
+
+    lines = lib.str_to_lines_no_empty(open("i12.txt").read())
+    print("Solution 1:", solve(lines))
+
+    lines = lib.str_to_lines_no_empty(EXAMPLE)
+    print("Example  2:", solve2(lines))
+
+    lines = lib.str_to_lines_no_empty(open("i12.txt").read())
+    print("Solution 2:", solve2(lines))
+
+if __name__ == "__main__":
+    main()