Solve day 25 and AoC 2022. Cool.

README.md

@@ -1,4 +1,11 @@
-# Times
+Done with this. Overall everything is solvable. It's more about consistency
+and focus. Of course, learning more algorithms and techniques helps.
+
+Possible to-dos:
+
+- [ ] Optimize day 19 because it is terrible.
+
+# Times (and comments)
 
 - Day  1: 7:52 ... so slow brah :/ top 100 required 2:05...
 - Day  2: 22:30 ... I mistyped the first and second was just bad top 100 would
@@ -33,4 +40,5 @@
   because I loose focus and make silly errors. Like back in Middleschool.
 - Day 24: Easy. Should have been faster, but no crazy mistakes. Still way too
   slow for something easy like this.
-- Day 25:
+- Day 25: Quickly solved via constraint solver. Actual solution much simpler. Don't know
+  if I would have been able to figure it out.

d25.py

@@ -0,0 +1,82 @@
+from lib import *
+
+EXAMPLE = """1=-0-2
+12111
+2=0=
+21
+2=01
+111
+20012
+112
+1=-1=
+1-12
+12
+1=
+122
+"""
+
+def snafu_to_dec(n: str) -> int:
+    r = 0
+    for i, c in enumerate(reversed(n)):
+        c = "=-012".index(c) - 2
+        r += c * 5**i
+    return r
+
+def dec_to_snafu(n: int) -> str:
+    r = ""
+    while n != 0:
+        rem = n % 5
+        n //= 5
+        if rem <= 2:
+            r = str(rem) + r
+        else:
+            r = "   =-"[rem] + r
+            n += 1
+    return r
+
+def dec_to_snafu_cs(n: int) -> str:
+    import cpmpy as cp
+    import numpy as np
+    size = 20
+    xs = cp.intvar(-2, 2, shape=size, name="xs")
+    ns = np.array([5**i for i in range(size)])
+    m = cp.Model(cp.sum(ns * xs) == n)
+    m.solve()
+
+    value = xs.value()
+    assert value is not None
+    # print(value)
+
+    r = ""
+    for v in value:
+        if v >= 0:
+            r += str(v)
+        elif v == -1:
+            r += "-"
+        elif v == -2:
+            r += "="
+        else:
+            assert False
+    r = "".join(reversed(r))
+    r = r.lstrip("0")
+    return r
+
+def solve(input: Input):
+    res = 0
+    for s in input.lines():
+        d = snafu_to_dec(s)
+        res += d
+    try:
+        assert dec_to_snafu_cs(res) == dec_to_snafu(res)
+    except ModuleNotFoundError:
+        print("Install 'cpmpy' to solve with constraint solver.")
+    return dec_to_snafu(res)
+
+def main():
+    DAY_INPUT = "i25.txt"
+    print("Example  1:", solve(Input(EXAMPLE)))
+    print("Solution 1:", solve(Input(DAY_INPUT)))
+
+
+if __name__ == "__main__":
+    main()