Solution to problem 7 in Python

src/Year_2017/P7.py

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+# --- Day 7: Recursive Circus ---
+
+# Wandering further through the circuits of the computer, you come upon a tower
+# of programs that have gotten themselves into a bit of trouble. A recursive
+# algorithm has gotten out of hand, and now they're balanced precariously in a
+# large tower.
+
+# One program at the bottom supports the entire tower. It's holding a large
+# disc, and on the disc are balanced several more sub-towers. At the bottom of
+# these sub-towers, standing on the bottom disc, are other programs, each
+# holding their own disc, and so on. At the very tops of these
+# sub-sub-sub-...-towers, many programs stand simply keeping the disc below
+# them balanced but with no disc of their own.
+
+# You offer to help, but first you need to understand the structure of these
+# towers. You ask each program to yell out their name, their weight, and (if
+# they're holding a disc) the names of the programs immediately above them
+# balancing on that disc. You write this information down (your puzzle input).
+# Unfortunately, in their panic, they don't do this in an orderly fashion; by
+# the time you're done, you're not sure which program gave which information.
+
+# For example, if your list is the following:
+
+# pbga (66)
+# xhth (57)
+# ebii (61)
+# havc (66)
+# ktlj (57)
+# fwft (72) -> ktlj, cntj, xhth
+# qoyq (66)
+# padx (45) -> pbga, havc, qoyq
+# tknk (41) -> ugml, padx, fwft
+# jptl (61)
+# ugml (68) -> gyxo, ebii, jptl
+# gyxo (61)
+# cntj (57)
+
+# ...then you would be able to recreate the structure of the towers that looks
+# like this:
+
+#                 gyxo
+#               /
+#          ugml - ebii
+#        /      \
+#       |         jptl
+#       |
+#       |         pbga
+#      /        /
+# tknk --- padx - havc
+#      \        \
+#       |         qoyq
+#       |
+#       |         ktlj
+#        \      /
+#          fwft - cntj
+#               \
+#                 xhth
+
+# In this example, tknk is at the bottom of the tower (the bottom program),
+# and is holding up ugml, padx, and fwft. Those programs are, in turn, holding
+# up other programs; in this example, none of those programs are holding up any
+# other programs, and are all the tops of their own towers. (The actual tower
+# balancing in front of you is much larger.)
+
+# Before you're ready to help them, you need to make sure your information is
+# correct. What is the name of the bottom program?
+
+with open("files/P7.txt") as f:
+    towers = [line for line in f.read().strip().split("\n")]
+
+
+def part_1():
+    parents, childs = [], []
+    for line in towers:
+        if "->" in line:
+            lhs, rhs = line.split(" -> ")
+            parent, _ = lhs.split()
+            parents.append(parent)
+            _childs = rhs.split(", ")
+            for child in _childs:
+                childs.append(child)
+        else:
+            parent, _ = line.split()
+            parents.append(parent)
+
+    root_program = list(set(parents) - set(childs))[0]
+
+    print(f"The name of the bottom program is {root_program}")
+
+
+if __name__ == "__main__":
+    part_1()