2 files changed, 33 insertions, 0 deletions
diff --git a/day15/day15.py b/day15/day15.py
new file mode 100644
index 0000000..a5660a4
--- /dev/null
+++ b/day15/day15.py
@@ -0,0 +1,32 @@
+"""Day 15."""
+
+
+# reading off numbers
+# starting numbers in input
+# consider the most recently spoken number
+
+# new unique numbers mean the current says zero
+# how far aprat the previous spoken one was
+
+
+with open("input") as f:
+    memory = list(map(int, f.read().rstrip().split(",")))
+
+last_pos = {val: pos + 1 for pos, val in enumerate(memory)}
+
+pos = len(memory) + 1
+for x in range(2020 - pos + 1):
+    last = memory[-1]
+    if memory.count(last) == 1:
+        memory.append(0)
+    else:
+        x = pos - 1
+        y = last_pos[last]
+        val = x - y
+        memory.append(val)
+        last_pos[last] = x
+        if val not in last_pos:
+            last_pos[val] = pos
+    pos += 1
+
+print(memory[-1])
diff --git a/day15/input b/day15/input
new file mode 100644
index 0000000..6557303
--- /dev/null
+++ b/day15/input
@@ -0,0 +1 @@
+0,5,4,1,10,14,7