Solve day 20.

2017/d20.py

@@ -0,0 +1,55 @@
+from lib import str_to_ints
+from collections import defaultdict
+
+
+def part_1(data):
+    ps = []
+    for i, line in enumerate(data.splitlines()):
+        ps.append(str_to_ints(line) + [i])
+
+    for _ in range(10_000):
+        for p in ps:
+            p[3] += p[6]
+            p[4] += p[7]
+            p[5] += p[8]
+            p[0] += p[3]
+            p[1] += p[4]
+            p[2] += p[5]
+    
+    ps.sort(key=lambda p: abs(p[0]) + abs(p[1]) + abs(p[2]))
+    print(ps[0][-1])
+
+
+def part_2(data):
+    ps = []
+    for i, line in enumerate(data.splitlines()):
+        ps.append(str_to_ints(line) + [i])
+
+    for _ in range(10_000):
+        poss = defaultdict(list)
+
+        for p in ps:
+            p[3] += p[6]
+            p[4] += p[7]
+            p[5] += p[8]
+            p[0] += p[3]
+            p[1] += p[4]
+            p[2] += p[5]
+            poss[(p[0], p[1], p[2])].append(p)
+
+        for pts in poss.values():
+            if len(pts) > 1:
+                for p in pts:
+                    ps.remove(p)
+    
+    print(len(ps))
+
+
+def main():
+    data = open(0).read()
+    part_1(data)
+    part_2(data)
+
+
+if __name__ == "__main__":
+    main()

README.md

@@ -80,4 +80,5 @@ written in Python.
 - Day 17: 55:00
 - Day 18: 23:00
 - Day 19: 45:00
-- Day 20:
+- Day 20: 9:55 (would have been 10th)
+- Day 21: