From 525a0046b758ba54c5a6b54c14fccd24579064e1 Mon Sep 17 00:00:00 2001
From: Yuchen Pei <me@ypei.me>
Date: Sat, 23 Dec 2017 12:08:15 +0100
Subject: finished Day 23

---
 Puzzle23               | Bin 0 -> 34392 bytes
 Puzzle23.hi            | Bin 0 -> 1848 bytes
 Puzzle23.hs            |  33 ++++++++++++++++++++++++++++++++
 Puzzle23.o             | Bin 0 -> 25264 bytes
 Puzzle23translation.md |  51 +++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 84 insertions(+)
 create mode 100755 Puzzle23
 create mode 100644 Puzzle23.hi
 create mode 100644 Puzzle23.hs
 create mode 100644 Puzzle23.o
 create mode 100644 Puzzle23translation.md

diff --git a/Puzzle23 b/Puzzle23
new file mode 100755
index 0000000..fb77037
Binary files /dev/null and b/Puzzle23 differ
diff --git a/Puzzle23.hi b/Puzzle23.hi
new file mode 100644
index 0000000..4ef63d0
Binary files /dev/null and b/Puzzle23.hi differ
diff --git a/Puzzle23.hs b/Puzzle23.hs
new file mode 100644
index 0000000..e00afb2
--- /dev/null
+++ b/Puzzle23.hs
@@ -0,0 +1,33 @@
+import Data.List.Split (splitOn)
+import Data.Map (Map)
+import qualified Data.Map as Map
+
+exec :: [[Char]] -> Int -> Int -> Map Char Int -> Int
+exec rom n addr regs
+  | addr >= length rom || addr < 0 = n
+  | op == "set" = exec rom n (addr + 1) (Map.insert dest val regs)
+  | op == "sub" = exec rom n (addr + 1) (Map.insert dest (dval - val) regs)
+  | op == "mul" = exec rom (n + 1) (addr + 1) (Map.insert dest (dval * val) regs)
+  | op == "jnz" = exec rom n (if dval /= 0 then addr + val else addr + 1) regs
+      where ins = rom !! addr
+            op:[dest]:xs = splitOn " " ins
+            dval = getVal [dest]
+            val = getVal $ head xs
+            getVal xs = if head xs `elem` alphabet then regs Map.! (head xs) else read xs
+
+isPrime :: Int -> Bool
+isPrime x = and $ ((/=0) . rem x) <$> [2 .. floor $ sqrt $ fromIntegral x]
+
+solve2 = length $ filter (==False) $ isPrime <$> [105700, 105717 .. 122700] -- The last number, 122700 should not be included because according to the assembly code when b == c the program terminates without checking primality of b. But the AOC website only accepted the answer when it is included.
+
+alphabet = ['a'..'h']
+
+initRegs :: Map Char Int
+initRegs = Map.fromList $ zip ['a'..'h'] (cycle [0])
+
+
+solve1 :: [Char] -> Int
+solve1 xs = exec (lines xs) 0 0 initRegs
+
+
+input = "set b 57\nset c b\njnz a 2\njnz 1 5\nmul b 100\nsub b -100000\nset c b\nsub c -17000\nset f 1\nset d 2\nset e 2\nset g d\nmul g e\nsub g b\njnz g 2\nset f 0\nsub e -1\nset g e\nsub g b\njnz g -8\nsub d -1\nset g d\nsub g b\njnz g -13\njnz f 2\nsub h -1\nset g b\nsub g c\njnz g 2\njnz 1 3\nsub b -17\njnz 1 -23"
diff --git a/Puzzle23.o b/Puzzle23.o
new file mode 100644
index 0000000..fd2fdef
Binary files /dev/null and b/Puzzle23.o differ
diff --git a/Puzzle23translation.md b/Puzzle23translation.md
new file mode 100644
index 0000000..018e129
--- /dev/null
+++ b/Puzzle23translation.md
@@ -0,0 +1,51 @@
+Translation from the assembly code to pseudocode:
+
+'''
+b = 105700
+c = 122700
+
+for b = 105700, 105717, .., 122683
+    f = 1
+    for d = 2 .. b
+        for e = 2 .. b
+            if d * e == b then f = 0
+    if f == 0 then h += 1
+return h
+'''
+
+The original assembly code:
+
+'''
+set b 57
+set c b
+jnz a 2
+jnz 1 5
+mul b 100
+sub b -100000
+set c b
+sub c -17000
+set f 1
+set d 2
+set e 2
+set g d
+mul g e
+sub g b
+jnz g 2
+set f 0
+sub e -1
+set g e
+sub g b
+jnz g -8
+sub d -1
+set g d
+sub g b
+jnz g -13
+jnz f 2
+sub h -1
+set g b
+sub g c
+jnz g 2
+jnz 1 3
+sub b -17
+jnz 1 -23
+'''
-- 
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