day 10

2 files changed, 48 insertions, 0 deletions

diff --git a/20/README b/20/README
index 907211d..b70ace7 100644
--- a/20/README
+++ b/20/README
@@ -11,6 +11,7 @@ Day     Time            Ans     Time            Ans
   7    2.884            139    2.681          58175
   8    0.263           2025    1.193            826
   9    2.741       26796446    2.875        3353494
+ 10    0.027           2046    0.161  1157018619904
       -------                 -------
 tot    TBD                     TBD
 
@@ -19,6 +20,7 @@ Stats:
 
       -------Part 1--------   -------Part 2--------
 Day       Time  Rank  Score       Time  Rank  Score
+ 10   00:08:17  1496      0   00:51:01  2766      0
   9   00:25:55  6220      0   00:31:44  4392      0
   8   00:08:21  1632      0   00:17:34  1265      0
   7   00:55:51  5031      0   01:03:46  3520      0
diff --git a/20/py/d10.py b/20/py/d10.py
new file mode 100644
index 0000000..2b3bc2e
--- /dev/null
+++ b/20/py/d10.py
@@ -0,0 +1,46 @@
+#!/usr/bin/env python3
+import aoc20
+import functools
+import sys
+
+
+def pt1(_in):
+    jolts = [int(n.strip()) for n in _in]
+    jolts.append(max(jolts)+3)
+    jolts = sorted(jolts)
+    jolt = 0
+    diffs = [0, 0, 0]
+    for j in jolts:
+        diffs[j-jolt-1] += 1
+        jolt = j
+    return diffs[0] * diffs[2]
+
+
+def pt2(_in):
+    jolts = [int(n.strip()) for n in _in]
+    jolts.append(max(jolts)+3)
+    jolts = sorted(jolts)
+    jolts.insert(0, 0)
+    jolt = 0
+    reach = {}
+    for i in range(len(jolts)):
+        reachable = []
+        j = i+1
+        while j < len(jolts) and jolts[j] - jolts[i] <= 3:
+            reachable.append(jolts[j])
+            j += 1
+        reach[jolts[i]] = tuple(reachable)
+
+    @functools.cache
+    def ways(start, dest):
+        if start == dest:
+            return 1
+        return sum(ways(child, dest) for child in reach[start])
+
+    return ways(jolts[0], jolts[-1])
+
+
+if __name__ == "__main__":
+    input = aoc20.read_input(sys.argv[1:], 10)
+    print(pt1(input))
+    print(pt2(input))