Solution: Day 7 - part 1 & 2

Author: Kaba8081

solutions/2025/7/main.py

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+# 'Advent of code' solution for year 2025 day 7
+import os
+import sys
+
+DIR_PATH = os.path.dirname(os.path.realpath(__file__))
+
+def _get_input():
+    content = None
+    if os.path.isfile(os.path.join(DIR_PATH, "input.txt")):
+        with open(os.path.join(DIR_PATH, "input.txt"), "r", encoding="utf-8") as file:
+            content = file.read().strip().splitlines()
+        return content
+    else:
+        print("Error! Input file does not exist!")
+        sys.exit()
+
+def part_1(i: list[str]):
+    result = 0
+    curr = set()
+
+    curr.add(i[0].find("S"))
+    for line_i, line in enumerate(i[1:], 1):
+        new_curr = set()
+        for index in curr:
+            if line[index] == '^':
+                if index-1 >= 0 and line[index-1] == ".": # split left
+                    line = line[:index-1] + "|" + line[index:]
+                    new_curr.add(index-1)
+                if index+1 <= len(line) and line[index+1] == ".": # split right
+                    line = line[:index+1] + "|" + line[index+2:]
+                    new_curr.add(index+1)
+                result+=1
+            elif i[line_i][index] == ".":
+                line = line[:index] + "|" + line[index+1:]
+                new_curr.add(index)
+        curr = new_curr
+        i[line_i] = line
+
+        # print("\n".join(i), "\n")
+
+    print(f"[P1] Beam was split {result} times")
+
+def part_2(i: list[str]):
+    found: dict[tuple[int, int], int] = {}
+    splitters: dict[int, list[int]] = {}
+
+    for y, line in enumerate(i):
+        for x, val in enumerate(line):
+            if val == "^":
+                if x not in splitters:
+                    splitters[x] = []
+                splitters[x].append(y)
+
+    def rec(x: int, y: int) -> int:
+        if (x,y) in found:
+            return found[(x,y)]
+
+        split: int | None = None
+        if x in splitters and y < max(splitters[x]):
+            for sy in splitters[x]:
+                if sy > y:
+                    split = sy
+                    break
+
+        if split is None:
+            return 1
+
+        l = rec(x-1, split)
+        r = rec(x+1, split)
+
+        found[(x,y)] = l + r
+        return l + r
+
+    result = rec(i[0].find("S"), 0)
+    print(f"[P2] Beam was split {result} times")
+
+if __name__ == "__main__":
+    inputs = _get_input()
+    if not inputs:
+        print("Error! Input file is empty!")
+        sys.exit()
+
+    part_1(inputs.copy())
+    part_2(inputs.copy())
+
+    sys.exit()