[py] Port 2017_09

py/aoc/y2017/d09.py

@@ -0,0 +1,88 @@
+class Stream:
+    def __init__(self, string):
+        self.content = list(string)
+        self.content.reverse()
+
+    def peek(self):
+        return self.content[-1]
+
+    def pop(self):
+        return self.content.pop()
+
+
+def load_groups(inputstr):
+    groups = []
+    for line in inputstr.splitlines():
+        stream = Stream(line)
+        group, garbage = parse_group(stream)
+        groups.append((group, garbage))
+    return groups
+
+
+def parse_group(stream):
+    assert stream.pop() == "{"
+
+    if stream.peek() == "}":
+        assert stream.pop() == "}"
+        return [], 0
+
+    groups = []
+    garbage = 0
+
+    while True:
+        # Determine which sub-parser to use
+        if stream.peek() == "{":
+            group, more_garbage = parse_group(stream)
+            groups.append(group)
+            garbage += more_garbage
+        elif stream.peek() == "<":
+            garbage += parse_garbage(stream)
+        else:
+            raise Exception("Incorrectly formatted input")
+
+        # Determine whether to stop parsing
+        if stream.peek() == "}":
+            break
+        elif stream.peek() == ",":
+            assert stream.pop() == ","
+        else:
+            raise Exception("Incorrectly formatted input")
+
+    assert stream.pop() == "}"
+    return groups, garbage
+
+
+def parse_garbage(stream):
+    assert stream.pop() == "<"
+
+    escaped = False
+    garbage = 0
+
+    while True:
+        if escaped:
+            stream.pop()
+            escaped = False
+        elif stream.peek() == "!":
+            assert stream.pop() == "!"
+            escaped = True
+        elif stream.peek() == ">":
+            break
+        else:
+            stream.pop()
+            garbage += 1
+
+    assert stream.pop() == ">"
+
+    return garbage
+
+
+def group_score(group, level=1):
+    return sum(group_score(subgroup, level + 1) for subgroup in group) + level
+
+
+def solve(inputstr):
+    groups = load_groups(inputstr)
+    for group, garbage in groups:
+        score = group_score(group)
+        print(f"Part 1: {score}")
+        print(f"Part 2: {garbage}")