From 94ccfd4e183a0e18bd89a76b4b4def7c741b5636 Mon Sep 17 00:00:00 2001
From: Andrew Ekstedt <andrew.ekstedt@gmail.com>
Date: Tue, 2 Dec 2025 08:06:03 +0000
Subject: [PATCH] day 2 refactor

---
 day02/sol.py | 82 ++++++++++++++++++++++++----------------------------
 1 file changed, 38 insertions(+), 44 deletions(-)

diff --git a/day02/sol.py b/day02/sol.py
index eed97da..7add81a 100644
--- a/day02/sol.py
+++ b/day02/sol.py
@@ -11,7 +11,7 @@ def solve(input):
 
     t = 0
     for lo,hi in ranges:
-        invalid = list(findinvalid(lo,hi))
+        invalid = list(findinvalid(lo,hi,1))
         #if len(invalid) == 0:
         #    print(lo,hi,invalid)
         t += sum(invalid)
@@ -19,53 +19,47 @@ def solve(input):
 
     t2 = 0
     for lo,hi in ranges:
-        invalid2 = set(findinvalid2(lo,hi))
+        invalid2 = set(findinvalid(lo,hi,2))
         t2 += sum(invalid2)
     print(t2)
 
-def findinvalid(lo, hi):
-    assert len(str(hi)) - len(str(lo)) <= 1
+def findinvalid(lo, hi, part):
     assert lo <= hi
-    j = len(str(lo)) // 2
-    if j < 1:
-        # (1,19) => [11]
-        j = 1
-    for B in [10**j, 10**(j+1)]:
-        for i in range(lo//B, hi//B+1):
-            if i < B//10:
-                continue
-            if i >= B:
-                break
-            id = i*B + i
-            if lo <= id <= hi:
-                assert(str(i)+str(i) == str(id)), (i,id)
-                #print(lo, hi, i,B,id)
-                yield id
+    if log10(hi) != log10(lo):
+        assert log10(hi) - log10(lo) == 1
+        yield from findinvalid(lo,exp10(log10(lo))-1, part)
+        yield from findinvalid(exp10(log10(hi)-1),hi, part)
+    elif part == 1:
+        N = log10(hi)
+        if N % 2 == 0:
+            d = N // 2
+            yield from _find(lo,hi,d,N)
+    elif part == 2:
+        N = log10(hi)
+        for d in range(1,N):
+            if N%d == 0:
+                yield from _find(lo,hi,d,N)
 
-def findinvalid2(lo, hi):
-    assert lo <= hi,(lo,hi)
-    if len(str(hi)) != len(str(lo)):
-        assert len(str(hi)) - len(str(lo)) == 1
-        yield from findinvalid2(lo,10**len(str(lo))-1)
-        yield from findinvalid2(10**(len(str(hi))-1),hi)
-        return
-    N = len(str(hi))
-    for d in range(1,N):
-        if N%d == 0:
-            B = 10**d
-            BB = 10**(N-d)
-            factor = sum(10**k for k in range(0,N,d))
-            for i in range(lo//BB, hi//BB+1):
-                if i < B//10:
-                    continue
-                if i >= B:
-                    break
-                id = i*factor
-                #print(lo,hi,factor,i,id)
-                if lo <= id <= hi:
-                    #assert(str(i)*(N//d) == str(id)), (i,id)
-                    #print(lo, hi, i,B,id)
-                    yield id
+def _find(lo, hi, d, N):
+    B = exp10(d)
+    BB = exp10(N-d)
+    factor = sum(exp10(k) for k in range(0,N,d))
+    for i in range(lo//BB, hi//BB+1):
+        if i < B//10:
+            continue
+        if i >= B:
+            break
+        id = i*factor
+        if lo <= id <= hi:
+            #assert(str(i)*(N//d) == str(id)), (i,id)
+            #print(lo, hi, i,B,id)
+            yield id
 
-#solve("sample")
+def exp10(n):
+    return 10 ** n
+
+def log10(n):
+    return len(str(n))
+
+solve("sample")
 solve("input")