Solve day 9

2020/day09-xmas.py

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+import copy
+import itertools
+from typing import List
+
+
+def main(
+    filename: str,
+    expected_part_1: int = None,
+    expected_part_2: int = None,
+    preamble: int = 25,
+):
+    print(f"\n+ Running on {filename}")
+    with open(filename) as f:
+        numbers = list(map(int, f.read().strip().split("\n")))  # type: List[int]
+
+    pointer = preamble
+    while pointer < len(numbers) and matches_rule(numbers, pointer, preamble):
+        pointer += 1
+
+    counter_part_1 = numbers[pointer]
+    range_part_2 = sorted(find_range(numbers, counter_part_1))
+    counter_part_2 = range_part_2[0] + range_part_2[-1]
+
+    print(f"1. Found {counter_part_1}")
+    if expected_part_1:
+        assert expected_part_1 == counter_part_1
+
+    print(f"2. Found {counter_part_2}")
+    if expected_part_2:
+        assert expected_part_2 == counter_part_2
+
+
+def matches_rule(numbers, pointer, preamble):
+    range_start = pointer - preamble
+    range_end = pointer
+    number = numbers[pointer]
+    for combination in itertools.combinations(numbers[range_start:range_end], 2):
+        if number == sum(combination):
+            return True
+    return False
+
+
+def find_range(numbers, found_in_step_1):
+    for i, start in enumerate(numbers):
+        total = start
+        j = i + 1
+        while total < found_in_step_1 and j < len(numbers):
+            total += numbers[j]
+            j += 1
+        if total == found_in_step_1:
+            return numbers[i:j]
+    raise Exception("Didn't find a valid range")
+
+
+if __name__ == "__main__":
+    main("inputs/day09-test1", 127, 62, preamble=5)
+    main("inputs/day09", 144381670)

2020/inputs/day09-test1

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+35
+20
+15
+25
+47
+40
+62
+55
+65
+95
+102
+117
+150
+182
+127
+219
+299
+277
+309
+576