Add solution 3

Author: EmilyBZhang

rounds/3_dna/solution.py

@@ -5,13 +5,41 @@
 own faster implementation.
 """
 
-from .baseline import find_matches as _baseline
+from concurrent.futures import ThreadPoolExecutor
+
+
+def _find_matches(pattern_str: str, record: str) -> tuple[str, list[int]]:
+    lines = record.split("\n")
+    record_id = lines[0].strip()
+    sequence = "".join(lines[1:]).replace(" ", "")
+
+    positions: list[int] = []
+    start = 0
+    while True:
+        pos = sequence.find(pattern_str, start)
+        if pos == -1:
+            break
+        positions.append(pos)
+        start = pos + 1
+
+    return (record_id, positions)
 
 
 def find_matches(fasta_path: str, pattern: bytes) -> list[tuple[str, list[int]]]:
     """Find every FASTA record whose sequence contains ``pattern``.
 
     Returns ``[(record_id, [positions...]), ...]`` in file order.
     """
-    # TODO: remove this delegation and write your own implementation here.
-    return _baseline(fasta_path, pattern)
+    pattern_str = pattern.decode("ascii")
+    matches = []
+    with open(fasta_path, "r") as f:
+        text = f.read()
+
+    with ThreadPoolExecutor(16) as ex:
+        futures = [
+            ex.submit(_find_matches, pattern_str, record)
+            for record in text.split(">")
+            if record.strip()
+        ]
+        matches = [res for future in futures if (res := future.result())[1]]
+    return matches