diff --git a/2020-python/solutions/day_9.py b/2020-python/solutions/day_9.py
index ac2d4c7..6b24d1a 100644
--- a/2020-python/solutions/day_9.py
+++ b/2020-python/solutions/day_9.py
@@ -48,16 +48,17 @@ def part1(entries: list, preamble_length: int) -> int:
 
 def part2(entries: list, invalid_number: int) -> int:
     """part2 solver"""
-    for index, _ in enumerate(entries):
-        test_set = [entries[index]]
-        test_set_len = 1
-        while test_set_len < len(entries) - index:
-            test_set.append(entries[index+test_set_len])
-            test_set_len += 1
-
-            if sum(test_set) == invalid_number:
-                return min(test_set) + max(test_set)
-    return None
+    left, right = 0, 1
+    interval_sum = entries[left] + entries[right]
+    while True:
+        if interval_sum < invalid_number:
+            right += 1
+            interval_sum += entries[right]
+        elif interval_sum > invalid_number:
+            interval_sum -= entries[left]
+            left += 1
+        else:
+            return min(entries[left:right+1]) + max(entries[left:right+1])
 
 def test_input_day_9():
     """pytest testing function"""
diff --git a/README.md b/README.md
index ee3df75..1927ccb 100644
--- a/README.md
+++ b/README.md
@@ -16,8 +16,8 @@
 | [Day 4](https://adventofcode.com/2020/day/4) | [21.806ms](./2020-python/solutions/day_4.py)  |
 | [Day 5](https://adventofcode.com/2020/day/5) | [5.993ms](./2020-python/solutions/day_5.py)   |
 | [Day 6](https://adventofcode.com/2020/day/6) | [2.587ms](./2020-python/solutions/day_6.py)   |
-| [Day 7](https://adventofcode.com/2020/day/7) | [1.689ms](./2020/python/solutions/day_7.py)   |
-| [Day 8](https://adventofcode.com/2020/day/8) | [6.313ms](./2020/python/solutions/day_8.py)   |
-| [Day 9](https://adventofcode.com/2020/day/9) | [552.396ms](./2020/python/solutions/day_9.py) |
+| [Day 7](https://adventofcode.com/2020/day/7) | [1.689ms](./2020-python/solutions/day_7.py)   |
+| [Day 8](https://adventofcode.com/2020/day/8) | [6.313ms](./2020-python/solutions/day_8.py)   |
+| [Day 9](https://adventofcode.com/2020/day/9) | [7.2207ms](./2020-python/solutions/day_9.py) |