[2021] solve day 3 python

2021/Python/day03.py

@@ -0,0 +1,59 @@
+from typing import DefaultDict
+
+
+def load_input() -> list[str]:
+    with open('../.input/day03', 'r') as f:
+        return [line.strip() for line in f.readlines()]
+
+
+def solve1() -> int:
+    input = load_input()
+    cache = [{"0": 0, "1": 0} for _ in range(len(input[0]))]
+
+    for binary in input:
+        for i, c in enumerate(binary):
+            cache[i][c] += 1
+    
+    gamma, epsilon = map(sum, zip(*[
+        (2**i, 0) if c["1"] > c["0"] else (0, 2**i)
+        for i, c in enumerate(reversed(cache))
+    ]))
+    return gamma * epsilon
+
+
+def find_single(input: list[str], reverse: bool = False) -> int:
+    cache = [{"0": 0, "1": 0} for _ in range(len(input[0]))]
+    remaining = input[:]
+    
+    for binary in remaining:
+        for i, digit in enumerate(binary):
+            cache[i][digit] += 1
+    
+    for i, c in enumerate(cache):
+        if len(remaining) == 1:
+            break
+
+        generator = (entry for entry in remaining)
+        remaining = []
+        winning_digit = ("0" if c["0"] <= c["1"] else "1") if reverse else ("1" if c["1"] >= c["0"] else "0")
+        for binary in generator:
+            if binary[i] == winning_digit:
+                remaining.append(binary)
+            else:
+                for digit, cache_dict in zip(binary, cache):
+                    cache_dict[digit] -= 1
+    
+    return remaining[0]
+
+
+def solve2() -> int:
+    input = load_input()
+    oxygen, carbon = input[:], input[:]
+    res_o = sum(2**int(i) for i, x in enumerate(reversed(find_single(oxygen, reverse=False))) if x == "1")
+    res_c = sum(2**int(i) for i, x in enumerate(reversed(find_single(carbon, reverse=True))) if x == "1")
+    return res_o * res_c
+
+
+if __name__ == "__main__":
+    print(solve1())
+    print(solve2())