Add solution for day 3

src/day03.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+
+from re import finditer
+from util import print_color, read_input, Color
+
+
+mul_pattern = "mul\\(([0-9]{1,3},[0-9]{1,3})\\)"
+do_pattern = "do(n't)?\\(\\)"
+combined_pattern = f"({mul_pattern}|{do_pattern})"
+
+
+def part1(input_lines):
+    total = 0
+    for line in input_lines:
+        matches = finditer(mul_pattern, line)
+        for match in matches:
+            (left, right) = map(lambda x: int(x), match.group(1).split(","))
+            total += left * right
+    return total
+
+
+def part2(input_lines):
+    total = 0
+    enabled = True
+    matches = []
+    for line in input_lines:
+        matches += list(finditer(combined_pattern, line))
+    i = 0
+    while i < len(matches):
+        old_total = total
+        match = matches[i]
+        color = Color.GREY
+        if match.group(0) == "do()":
+            enabled = True
+        elif match.group(0) == "don't()":
+            enabled = False
+        else:
+            color = Color.GREEN if enabled else Color.RED
+            if enabled:
+                (left, right) = map(lambda x: int(x), match.group(2).split(","))
+                total += left * right
+        print_color(f'{i}: {match.group(0)} - {old_total} -> {total}', color)
+        i += 1
+    return total
+
+
+test_input = read_input("_test")
+assert 161 == part1(test_input)
+
+real_input = read_input()
+print(part1(real_input))
+
+test_input_2 = read_input("_test_2")
+assert 48 == part2(test_input_2)
+print(part2(real_input))