Solve day 3 part 1

year_2023/day03/gear_ratios.py

@@ -1,8 +1,53 @@
 from util import read_puzzle_input
 
 
+def _is_symbol(char):
+    return char != "." and not char.isdigit()
+
+
+def _is_part_number(lines, line_num, start, end):
+    min_x = max(0, start - 1)
+    max_x = min(len(lines[0]), end + 1)
+
+    if line_num > 0:
+        # Check above
+        for x in range(min_x, max_x):
+            if _is_symbol(lines[line_num - 1][x]):
+                return True
+    if len(lines) > line_num + 1:
+        # Check below
+        for x in range(min_x, max_x):
+            if _is_symbol(lines[line_num + 1][x]):
+                return True
+
+    if _is_symbol(lines[line_num][min_x]) or _is_symbol(lines[line_num][max_x - 1]):
+        return True
+
+    return False
+
+
 def sum_part_numbers(puzzle_input):
-    return 0
+    lines = puzzle_input.split("\n")
+    potential_parts = []
+    for line_num, line in enumerate(lines):
+        i = 0
+        while i < len(line):
+            if line[i].isdigit():
+                num = ""
+                start = i
+                while i < len(line) and line[i].isdigit():
+                    num += line[i]
+                    i += 1
+                end = i
+                potential_parts.append((num, line_num, start, end))
+            else:
+                i += 1
+
+    answer = 0
+    for num, line_num, start, end in potential_parts:
+        if _is_part_number(lines, line_num, start, end):
+            answer += int(num)
+    return answer
 
 
 if __name__ == "__main__":