15.1

15/15.py

@@ -0,0 +1,74 @@
+test_input = """
+########
+#..O.O.#
+##@.O..#
+#...O..#
+#.#.O..#
+#...O..#
+#......#
+########
+
+<^^>>>vv<v>>v<<
+""".strip()
+
+
+def parse(input):
+    m, c = input.split("\n\n")
+    c = "".join(c.split("\n"))
+    m = list(map(list, m.split("\n")))
+    return m, c
+
+
+d = {"v": (1, 0), "^": (-1, 0), "<": (0, -1), ">": (0, 1)}
+
+
+def gps(c):
+    i, j = c
+    return i * 100 + j
+
+
+def start(m):
+    for i, row in enumerate(m):
+        for j, ch in enumerate(row):
+            if ch == "@":
+                return i, j
+    raise ValueError("no start position")
+
+
+def boxes(m):
+    for i, row in enumerate(m):
+        for j, ch in enumerate(row):
+            if ch == "O":
+                yield i, j
+
+
+def field(m):
+    return "\n".join("".join(y for y in x) for x in m)
+
+
+def part1(m, c):
+    ri, rj = start(m)
+    # print("1", ri, rj)
+    for ch in c:
+        di, dj = d[ch]
+        # print("2", di, dj)
+        move = True
+        ci = ri + di
+        cj = rj + dj
+        while move and m[ci][cj] != ".":
+            if m[ci][cj] == "#":
+                move = False
+            ci += di
+            cj += dj
+        # print("3", move, ci, cj)
+        if move:
+            m[ci][cj] = m[ri + di][rj + dj]
+            m[ri + di][rj + dj] = "@"
+            m[ri][rj] = "."
+            ri = ri + di
+            rj = rj + dj
+            # print(field(m))
+    return sum(map(gps, boxes(m)))
+
+
+print(part1(*parse(open("input").read())))