Day 7 of 2020 done in Python

2020/Day 7/Solution.py

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+import re
+
+bag_re = re.compile(r'(?:([a-z\s]+) bags contain)?(?:\s?([0-9]) ([a-z\s]+)\sbags?[,.])')
+
+input_file = "input.txt"
+
+
+def find_bags_containing_bag(search_bag="shiny gold"):
+    # Stores the bag colors that can store the bag in the key
+    bag_relations = {}
+
+    with open(input_file) as rules:
+        line = rules.readline()
+
+        while line and line != "\n":
+            match = bag_re.findall(line)
+
+            if not match:
+                line = rules.readline()
+                continue
+
+            parent_bag = match[0][0]
+
+            for sub_match in match:
+
+                if sub_match[2] in bag_relations and parent_bag not in bag_relations[sub_match[2]]:
+                    bag_relations[sub_match[2]].append(parent_bag)
+                else:
+                    bag_relations[sub_match[2]] = [parent_bag]
+
+            line = rules.readline()
+
+    explored_bags = []
+    bags_to_explore = [search_bag]
+
+    usable_bags = 0
+
+    while len(bags_to_explore) > 0:
+        current_exploration = bags_to_explore.pop(0)
+        explored_bags.append(current_exploration)
+
+        if current_exploration not in bag_relations:
+            continue
+
+        for bag in bag_relations[current_exploration]:
+            if bag not in explored_bags and bag not in bags_to_explore:
+                usable_bags += 1
+                bags_to_explore.append(bag)
+
+    print(f"The number of bags that can contain a {search_bag} bag is {usable_bags}")
+
+
+def count_bags_contained_in_bag(search_bag="shiny gold"):
+    # Stores the number of bags a bag directly contains
+    bag_counts = {}
+    # Stores the bags contained and how many of them
+    bags_contained = {}
+
+    with open(input_file) as rules:
+        line = rules.readline()
+
+        while line and line != "\n":
+            match = bag_re.findall(line)
+
+            if not match:
+                line = rules.readline()
+                continue
+
+            parent_bag = match[0][0]
+
+            bags_contained[parent_bag] = []
+            bag_counts[parent_bag] = 0
+
+            for sub_match in match:
+                bag_counts[parent_bag] += int(sub_match[1])
+                bags_contained[parent_bag].append((sub_match[2], int(sub_match[1])))
+
+            line = rules.readline()
+
+    explored_bags = []
+    bags_to_explore = [(search_bag, 1)]
+
+    total_bags = 0
+
+    # For each bag, fetch the total amount of bag it contains and multiply it by the number of times
+    # this bag has been counted. Then, add the contained bag to the list of bags to count while keeping track of
+    # the multiplier.
+    # For ex. : a bag contains two blue bags. The blue bags are added with a multiplier of two.
+    # The blue bags contain each three red bags. Thus, we count six red bags and add them with a multiplier of six.
+    while len(bags_to_explore) > 0:
+        current_exploration = bags_to_explore.pop(0)
+        explored_bags.append(current_exploration)
+
+        if current_exploration[0] not in bag_counts:
+            continue
+
+        # Add the number of bags contained, multiplied by the number of times this has appeared in this "bag descent"
+        total_bags += bag_counts[current_exploration[0]]*current_exploration[1]
+
+        for bag in bags_contained[current_exploration[0]]:
+            # Keep track of the number of bags that appear in total by multiplying the number of bags
+            # by the number of times the current bag appears in this "bag descent"
+            bags_to_explore.append((bag[0], current_exploration[1]*bag[1]))
+
+    print(f"The total number of bags a {search_bag} contains {total_bags}")