Use deque and Counter to speed up

Author: stefmolin

rounds/1_histogram/baseline.py

@@ -4,21 +4,10 @@
 tokens) in a binary payload.
 """
 
+from collections import Counter, deque
+from pathlib import Path
+
 
 def compute_histogram(path: str) -> dict[bytes, int]:
     """Frequency of every 2-byte bigram in the file at ``path``."""
-    # Step 1: read the whole file into memory as a single bytes object.
-    with open(path, "rb") as f:
-        data = f.read()
-
-    # Step 2: slide a 2-byte window across the buffer. For ``b"ABCD"`` the
-    # iterations produce ``b"AB"``, ``b"BC"``, then ``b"CD"``. For each window,
-    # bump the matching bucket in a ``dict`` keyed by the bigram itself.
-    counts: dict[bytes, int] = {}
-    for i in range(len(data) - 1):
-        bigram = data[i : i + 2]
-        if bigram in counts:
-            counts[bigram] += 1
-        else:
-            counts[bigram] = 1
-    return counts
+    return Counter(deque(Path(path).read_bytes(), maxlen=2))