Solve 2019:06 "Universal Orbit Map"

Tried to solve part 2 using BFS, but did not
figure out a way to find shortest path. Fell
back to a less elegant but more simple
approach.

2019-python/output/day_06.py

@@ -0,0 +1,46 @@
+from collections import defaultdict, deque
+from output import answer, puzzleinput
+
+n = 6
+title = "Universal Orbit Map"
+
+
+@puzzleinput(n)
+def parse_input(data):
+    heritage = defaultdict(str)
+    for parent, child in [line.split(")") for line in data.split()]:
+        heritage[child] = parent
+    return heritage
+
+
+@answer(1, "{} direct and indirect orbits")
+def part_1(heritage):
+    return sum(len(ancestry(heritage, v)) for v in heritage.keys())
+
+
+@answer(2, "Orbit transfers needed for you to share orbit with Santa: {}")
+def part_2(heritage):
+    a = ancestry(heritage, "YOU")
+    b = ancestry(heritage, "SAN")
+    shared = len(set(a) & set(b))
+    return sum(
+        [
+            len(a) - shared,
+            len(b) - shared,
+        ]
+    )
+
+
+def ancestry(parents, child):
+    k = child
+    lineage = []
+    while k in parents:
+        lineage.append(parents[k])
+        k = parents[k]
+    return lineage[::-1]
+
+
+if __name__ == "__main__":
+    parsed = parse_input()
+    part_1(parsed)
+    part_2(parsed)