day 17 python part 2 solve

day17/sol.py

@@ -7,8 +7,9 @@ rocks = [
     0b00011000_00011000,
 ]
 
-jets = itertools.cycle(">>><<><>><<<>><>>><<<>>><<<><<<>><>><<>>")
-jets = itertools.cycle(open("input").read().strip())
+jets = ">>><<><>><<<>><>>><<<>>><<<><<<>><>><<>>"
+
+jets = open("input").read().strip()
 
 rocki = itertools.cycle(rocks)
 
@@ -22,6 +23,7 @@ def drop(a, r, jets):
     h = a.bit_length() + 8*3
     if h % 8 != 0:
         h += 8 - h%8
+    numjets = 0
     while True:
         j = next(jets)
         if j == '<':
@@ -35,6 +37,7 @@ def drop(a, r, jets):
                 x >>= 8
                 if x & (a>>h) == 0:
                     r = x
+        numjets += 1
 
         # continue falling?
         if r & (a>>(h-8)) == 0:
@@ -43,19 +46,53 @@ def drop(a, r, jets):
         else:
             # stop
             a |= (r<<h)
-            return a
+            return a, numjets
 
 
 a = 0b11111111
 wall = 0b10000000_10000000_10000000_10000000_10000000
 stopped = 0
-while stopped < 2022:
+jeti = itertools.cycle(jets)
+i = 0
+j = 0
+seen = dict()
+def head(a):
+    h = a.bit_length()
+    h -= h % 8
+    x = (a>>h)&0xff
+    while h >= 8 and x != 0x7f:
+        h -= 8
+        x |= (a>>h)&0xff
+    if x == 0x7f:
+        return a>>h
+    return 0
+import math
+def height(a):
+    return math.ceil(a.bit_length()/8)
+try:
+    while True:
         r = next(rocki)
-    a = drop(a,r,jets)
+        a, n = drop(a,r,jeti)
         stopped += 1
+        i = (i+1) % len(rocks)
+        j = (j+n) % len(jets)
+        if (i,j,head(a)) in seen:
+            break
+        seen[(i,j,head(a))] = (a,stopped)
         #for i in reversed(range(0,a.bit_length(),8)):
         #    print("{:08b}".format((a>>i)&0xff))
         #print()
+    b, old = seen[(i,j,head(a))]
+    sdiff = stopped - old
+    hdiff = height(a) - height(b)
+    goal = 1000000000000
+    rounds, extra = divmod(goal - stopped, sdiff)
+    h = rounds*hdiff
+    for _ in range(extra):
+        r = next(rocki)
+        a, n = drop(a,r,jeti)
+    print(rounds*hdiff + height(a)-1)
+finally:
+    print(i, j, stopped)
 
-import math
 print(math.ceil((a>>8).bit_length()/8))