Day 15

day15/input.txt

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+0,13,16,17,1,10,6

day15/part1.py

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+#!/usr/bin/env python3
+
+from collections import defaultdict
+
+lines = (x.strip() for x in open("input.txt"))
+nums = defaultdict(list)
+TARGET = 2020
+
+for line in lines:
+    print(line)
+    turn = 0
+    last_spoken = 0
+    for starting in map(int, line.split(",")):
+        nums[starting] = [turn]
+        turn += 1
+        last_spoken = starting
+    for t in range(turn, TARGET):
+        last = nums[last_spoken]
+        if len(last) == 2:
+            n = last[1] - last[0]
+        else:
+            n = 0
+        nums[n] = nums[n][-1:] + [t]
+        last_spoken = n
+    print("->", last_spoken)

day15/part2.py

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+#!/usr/bin/env python3
+
+from collections import defaultdict
+
+lines = (x.strip() for x in open("input.txt"))
+nums = defaultdict(list)
+TARGET = 30000000
+
+for line in lines:
+    print(line)
+    turn = 0
+    last_spoken = 0
+    for starting in map(int, line.split(",")):
+        nums[starting] = [turn]
+        turn += 1
+        last_spoken = starting
+    for t in range(turn, TARGET):
+        last = nums[last_spoken]
+        if len(last) == 2:
+            n = last[1] - last[0]
+        else:
+            n = 0
+        nums[n] = nums[n][-1:] + [t]
+        last_spoken = n
+    print("->", last_spoken)