Do day 8 and add gcm and prime factors to lib.

d8.py

@@ -0,0 +1,105 @@
+import lib
+
+EXAMPLE = """
+LLR
+
+AAA = (BBB, BBB)
+BBB = (AAA, ZZZ)
+ZZZ = (ZZZ, ZZZ)
+"""
+
+EXAMPLE2 = """
+LR
+
+11A = (11B, XXX)
+11B = (XXX, 11Z)
+11Z = (11B, XXX)
+22A = (22B, XXX)
+22B = (22C, 22C)
+22C = (22Z, 22Z)
+22Z = (22B, 22B)
+XXX = (XXX, XXX)
+"""
+
+def solve(lines: list[str]):
+    res = 0
+    elems = {}
+    for (i, line) in enumerate(lines):
+        if i == 0:
+            first = list(line)
+        else:
+            left, pair = line.split("=")
+            left = left.strip()
+            pair = pair.replace("(", "").replace(")", "").strip().split(", ")
+            elems[left] = pair
+    i = 0
+    start = "AAA"
+    while start != "ZZZ":
+        dir = first[i % len(first)]
+        if dir == "L":
+            start = elems[start][0]
+        elif dir == "R":
+            start = elems[start][1]
+        else:
+            raise Exception("Unex")
+        i += 1
+
+    return i
+
+def solve2(lines: list[str]):
+    res = 0
+    elems = {}
+    starts = []
+    ends = {}
+    for (i, line) in enumerate(lines):
+        if i == 0:
+            first = list(line)
+        else:
+            left, pair = line.split("=")
+            left = left.strip()
+            if left.endswith("A"):
+                starts.append(left)
+            if left.endswith("Z"):
+                ends[left] = 0
+            pair = pair.replace("(", "").replace(")", "").strip().split(", ")
+            elems[left] = pair
+    i = 0
+    while True:
+        new_starts = []
+        for start in starts:
+            dir = first[i % len(first)]
+            if dir == "L":
+                new_starts.append(elems[start][0])
+            elif dir == "R":
+                new_starts.append(elems[start][1])
+            else:
+                raise Exception("Unex")
+        i += 1
+        for start in new_starts:
+            if start in ends and ends[start] == 0:
+                ends[start] = i
+        starts = new_starts
+
+        for e in ends.values():
+            if e == 0:
+                break
+        else:
+            break
+    # 25:00
+    return lib.lcm(ends.values())
+
+def main():
+    lines = lib.str_to_lines_no_empty(EXAMPLE)
+    print("Example  1:", solve(lines))
+
+    lines = lib.str_to_lines_no_empty(open("i8.txt").read())
+    print("Solution 1:", solve(lines))
+
+    lines = lib.str_to_lines_no_empty(EXAMPLE2)
+    print("Example  2:", solve2(lines))
+
+    lines = lib.str_to_lines_no_empty(open("i8.txt").read())
+    print("Solution 2:", solve2(lines))
+
+if __name__ == "__main__":
+    main()

lib.py

@@ -1,5 +1,37 @@
 import re
 
+def prime_factors(n):
+    """
+    Returns a list of prime factors for n.
+
+    :param n: number for which prime factors should be returned
+    """
+    factors = []
+    rest = n
+    divisor = 2
+    while rest % divisor == 0:
+        factors.append(divisor)
+        rest //= divisor
+    divisor = 3
+    while divisor * divisor <= rest:
+        while rest % divisor == 0:
+            factors.append(divisor)
+            rest //= divisor
+        divisor += 2
+    if rest != 1:
+        factors.append(rest)
+    return factors
+
+def lcm(numbers: list[int]) -> int:
+    fs = []
+    for n in numbers:
+        fs += prime_factors(n)
+    s = 1
+    fs = list(set(fs))
+    for f in fs:
+        s *= f
+    return s
+
 def str_to_single_int(line: str) -> int:
     line = line.replace(" ", "")
     r = re.compile(r"\d+")