Day 16

answers/16.txt

@@ -0,0 +1,2 @@
+509
+496

day16.nim

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+import sequtils, strutils
+
+let ops = [
+    proc(regs: seq[int], a,b: int): int = regs[a] + b,
+    proc(regs: seq[int], a,b: int): int = regs[a] + regs[b],
+
+    proc(regs: seq[int], a,b: int): int = regs[a] * b,
+    proc(regs: seq[int], a,b: int): int = regs[a] * regs[b],
+
+    proc(regs: seq[int], a,b: int): int = regs[a] and b,
+    proc(regs: seq[int], a,b: int): int = regs[a] and regs[b],
+
+    proc(regs: seq[int], a,b: int): int = regs[a] or b,
+    proc(regs: seq[int], a,b: int): int = regs[a] or regs[b],
+
+    proc(regs: seq[int], a,b: int): int = a,
+    proc(regs: seq[int], a,b: int): int = regs[a],
+
+    proc(regs: seq[int], a,b: int): int = cast[int](a > regs[b]),
+    proc(regs: seq[int], a,b: int): int = cast[int](regs[a] > b),
+    proc(regs: seq[int], a,b: int): int = cast[int](regs[a] > regs[b]),
+
+    proc(regs: seq[int], a,b: int): int = cast[int](a == regs[b]),
+    proc(regs: seq[int], a,b: int): int = cast[int](regs[a] == b),
+    proc(regs: seq[int], a,b: int): int = cast[int](regs[a] == regs[b]),
+]
+
+func toInstr(line: string): seq[int] = line.strip.split(" ").map(parseInt)
+func toRegisterSample(line: string): seq[int] = line.substr(9, line.len - 2).split(", ").map(parseInt)
+
+proc execute(regs: var seq[int], instr: seq[int], opcodes: array[16, proc(regs: seq[int], a,b: int): int]) =
+    regs[instr[3]] = opcodes[instr[0]](regs, instr[1], instr[2])
+
+var
+    before, instr, after: seq[int]
+    opPossibilities: array[16, array[16, bool]]
+    opMappings: array[16, proc(regs: seq[int], a,b: int): int]
+    threeOrMore = 0
+    step = 0
+    registers = @[0, 0, 0, 0]
+
+for line in readFile("data/16.txt").splitlines:
+    if step == 0 and line.len > 6 and line[0..5] == "Before":
+        before = line.toRegisterSample
+        step.inc
+    elif step == 1:
+        instr = line.toInstr
+        step.inc
+    elif step == 2:
+        after = line.toRegisterSample
+        var count = 0
+        for i, op in ops:
+            var actual: seq[int]
+            actual.shallowCopy(before)
+            actual[instr[3]] = op(before, instr[1], instr[2])
+            if actual == after:
+                count.inc
+            else:
+                opPossibilities[instr[0]][i] = true
+        if count >= 3:
+            threeOrMore.inc
+        step = 0
+    
+    if step == 0 and line.len > 5 and line[0].isdigit:
+        # First instruction found after the samples -- figure out which
+        # opcode belongs to which...
+        var found: array[16, bool]
+        while not found.all(proc(v: bool): bool = v):
+            for opcode, possibilities in opPossibilities:
+                let matrix = zip(possibilities, found)
+                if matrix.count((false, false)) == 1:
+                    let index = matrix.find((false, false))
+                    found[index] = true
+                    opMappings[opcode] = ops[index]
+        step = -1
+    
+    if step == -1:
+        registers.execute(line.toInstr, opMappings)
+
+echo threeOrMore
+echo registers[0]