Solve day 17.

.gitignore

@@ -1,3 +1,4 @@
+all.py
 __pycache__
 *.txt
 *.md

d17.py

@@ -0,0 +1,119 @@
+from lib import *
+
+EXAMPLE = """>>><<><>><<<>><>>><<<>>><<<><<<>><>><<>>"""
+
+ROCKS = [
+    [(0, 0), (0, 1), (0, 2), (0, 3)],
+    [(0, 1), (-1, 0), (-1, 1), (-1, 2), (-2, 1)],
+    [(0, 0), (0, 1), (0, 2), (-1, 2), (-2, 2)],
+    [(0, 0), (-1, 0), (-2, 0), (-3, 0)],
+    [(0, 0), (0, 1), (-1, 0), (-1, 1)],
+]
+
+def printfall(coords):
+    row_coords = list(map(lambda c: c[0], coords))
+    col_coords = list(map(lambda c: c[1], coords))
+    min_row, max_row = min(row_coords), max(row_coords)
+    min_col, max_col = min(col_coords), max(col_coords)
+
+    s = ""
+    for r in range(min_row, max_row + 1):
+        for c in range(min_col, max_col + 1):
+            s += "."
+        s += "\n"
+    g = Input(s).grid2()
+    for c in coords:
+        c = (c[0] + -min_row, c[1])
+        g[tuple(c)] = "#"
+    g.print()
+    print()
+
+def solve(input: Input, second=False):
+    BLOWS = list(input.text.strip())
+    width, blow_index = 7, 0
+
+    heighest = [0 for _ in range(width)]
+    rocks = set([(0, i) for i in range(width)])
+
+    if second:
+        target = 1000000000000
+        nhs = {}
+    else:
+        target = 2022
+
+    i = 0
+    while i < target:
+        rock = ROCKS[i % len(ROCKS)]
+        pos = (min(heighest) - 4, 2)
+
+        if second and i > 0 and all(abs(heighest[i] - heighest[i + 1]) <= 2 for i in range(len(heighest) - 1)):
+            # long winded code to find repeating sequence
+            nh = tuple([h - min(heighest) for h in heighest])
+            if nh in nhs:
+                nhs[nh].append((i, heighest[0]))
+            else:
+                nhs[nh] = [(i, heighest[0])]
+            xs = nhs[nh]
+            if len(xs) > 4 and all(xs[1][0] - xs[0][0] == xs[i + 1][0] - xs[i][0] for i in range(len(xs) - 1)):
+                # we found a repeating sequence and can skip forward
+                di = xs[-1][0] - xs[-2][0]
+                dh = xs[-1][1] - xs[-2][1]
+                repeat = (target - i) // di
+                i += repeat * di
+                heighest = [h + repeat * dh for h in heighest]
+                for c, r in enumerate(heighest):
+                    rocks.add((r, c))
+                nhs = {}
+                continue
+
+        falling = True
+        while falling:
+            blow = BLOWS[blow_index % len(BLOWS)]
+            blow_index += 1
+
+            dc = None
+            if blow == ">":
+                dc = 1
+            elif blow == "<":
+                dc = -1
+
+            for (ro, co) in rock:
+                r = pos[0] + ro
+                c = pos[1] + co + dc
+                if c < 0 or c >= width or (r, c) in rocks:
+                    break
+            else:
+                pos = (pos[0], pos[1] + dc)
+
+            for (ro, co) in rock:
+                r = pos[0] + ro + 1
+                c = pos[1] + co
+                if (r, c) in rocks:
+                    falling = False
+                    break
+            else:
+                pos = (pos[0] + 1, pos[1])
+
+        for (ro, co) in rock:
+            r = pos[0] + ro
+            c = pos[1] + co
+            rocks.add((r, c))
+            heighest[c] = min(heighest[c], r)
+
+        i += 1
+
+    return -min(heighest)
+
+def main():
+    _, day = extract_year_and_date(__file__)
+    DAY_INPUT = f"i{day}.txt"
+    print("Example  1:", solve(Input(EXAMPLE)))
+    s1 = solve(Input(DAY_INPUT))
+    assert s1 == 3102
+    print("Solution 1:", s1)
+    print("Example  2:", solve(Input(EXAMPLE), True))
+    print("Solution 2:", solve(Input(DAY_INPUT), True))
+    assert solve(Input(DAY_INPUT), True) == 1539823008825
+
+if __name__ == "__main__":
+    main()