day 23 ivy solution

part 2 is very slow; takes about ~2min on my machine

day23/sol.ivy

@@ -1,7 +1,8 @@
 )get "input.ivy"
 sample = 7 7 rho '....#..' '..###.#' '#...#.#' '.#...##' '#.###..' '##.#.##' '.#..#..'
 
-board = sample == '#'
+#board = sample == '#'
+board = input == '#'
 #board
 
 op north a = 1 flip a
@@ -11,6 +12,9 @@ op east a = -1 rot a
 
 #north 3 3 rho iota 9
 
+op lift a = (1,rho a) rho a
+op n moveNSWE a = (lift n flip a[1]), (lift (-n) flip a[2]), (lift n rot a[3]), (lift (-n) rot a[4])
+
 op a coalesce b =
     a: a
     b
@@ -22,43 +26,102 @@ op maybePad a =
     needsPad a: pad a
     a
 
+op maybePad1 a =
+    c1 = any a[1]
+    c2 = any a[(rho a)[1]]
+    c1 and c2: 0,a,0
+    c1: 0,a
+    c2: a,0
+    a
+
+op maybePad a =
+    a = maybePad1 a
+    (any a[;1]) or (any a[;(rho a)[2]]): transp maybePad1 transp a
+    a
 
 op smearWE a = a or (west a) or (east a)
 op smearNS a = a or (north a) or (south a)
-op lift a = (1,rho a) rho a
 
 op show a = (text ".#23456789"[1+a]),"\n-"
 
 M = 0
 
-a = maybePad board
-n = south smearWE a
-s = north smearWE a
-e = west smearNS a
-w = east smearNS a
-#n
+op axis1 a = 3 1 2 transp a
 
-p = 4 3 2 1
+op look a =
+    ns = lift smearNS a
+    we = lift smearWE a
+    -1 moveNSWE (we, we, ns, ns)
 
-C = (lift n) , (lift s) , (lift w) , (lift e)
-rho C
-canMove = a and or/ 3 1 2 transp C # can move if there is an elf nearby
-C2 = (not C) and (rho C) rho canMove # can move in a direction if not alone and there is no elf in that direction
-show C2
-P1 = max/ p * 3 1 2 transp C2  # select direction
-P2 = p o.== P1   # decompose into 4x?x? matrix
-P1; "\n-"
-C3 = (north P2[1]) + (south P2[2]) + (west P2[3]) + (east P2[4])
-C3; "\n-"
-notBlock = C3 == 1
-C4 = (lift south notBlock), (lift north notBlock), (lift east notBlock), (lift west notBlock)
-rho C4
-P3 = P2 and C4
-show P3
-moved = or/ 3 1 2 transp P3
-moved
-#a and not moved
-#show P3
-B = (a and not moved) + (north P3[1]) + (south P3[2]) + (west P3[3]) + (east P3[4])
-show a
-show B
+op dup4 a = (4,rho a) rho a
+
+# look in each direction
+# an elf can move in a direction if there is no elf in said direction and there is an elf somewhere nearby
+# returns a 4x(rho a) matrix
+op canMove a =
+    C = look a
+    (not C) and dup4 (a and or/axis1 C)
+
+
+# prepare moves
+# assign each move a priority and take the max
+# remove lower priority moves
+op p prepare choices =
+    best = max/ p * axis1 choices  # select best direction
+    p o.== best                    # decompose into 4x?x? matrix
+
+# count how many elves want to move to each square
+# filter out moves which conflict
+op unblocked moves =
+    open = 1 == +/axis1 1 moveNSWE moves
+    moves and -1 moveNSWE dup4 open
+
+priority = 4 3 2 1
+M = 0
+changed = 0
+
+op M round a =
+    a = maybePad a
+    moves = unblocked (M flip priority) prepare canMove a
+    moved = or/axis1 moves
+    changed; changed = +/, moved
+    b = (a and not moved) + +/axis1 1 moveNSWE moves
+    b
+
+op round a = M round a
+
+# this is implemented using globals
+# to store the board instead of recursion
+# in order to avoid keeping a bunch of large
+# intermediate values alive on the stack
+B = 0
+op i loop n =
+    i > n: i
+    changed; changed = 0
+    B = M round B
+    M = M - 1
+    changed == 0: i
+    (i+1) loop n
+
+op n rounds a =
+    B; B = a
+    M; M = 0
+    1 loop n
+    B
+
+op n numrounds a =
+    B; B = a
+    M; M = 0
+    1 loop n
+
+op score a =
+    a = maybePad a
+    n = */ (rho a) - 2
+    n - +/, a
+
+show round board
+show 10 rounds board
+score 10 rounds board
+
+1000 numrounds board
+#numrounds board