Solve 2023:11 "Cosmic Expansion"

2023-python/output/day_11.py

@@ -0,0 +1,63 @@
+from itertools import combinations
+from output import answer
+
+n = 11
+title = "Cosmic Expansion"
+
+
+@answer(1, "Sum of all galaxy shortest distances is {}")
+def part_1(data):
+    return data[0]
+
+
+@answer(2, "Exapanding by 1M, sum is {}")
+def part_2(data):
+    return data[1]
+
+
+def presolve(data):
+    m = data.splitlines()
+    er = set()
+    ec = set()
+    for i, r in enumerate(m):
+        if "#" not in r:
+            er.add(i)
+    for i, c in enumerate(zip(*m)):
+        if "#" not in c:
+            ec.add(i)
+    h = len(m)
+    w = len(m[0])
+    g1 = []
+    g2 = []
+    e = 1e6
+    for r in range(h):
+        for c in range(w):
+            if m[r][c] == "#":
+                ro = len(er & set(range(r)))
+                co = len(ec & set(range(c)))
+                g1.append((r + ro, c + co))
+                g2.append((ro * e + r - ro, co * e + c - co))
+    p1 = sum(
+        abs(rc1[0] - rc2[0]) + abs(rc1[1] - rc2[1]) for rc1, rc2 in combinations(g1, 2)
+    )
+    p2 = int(
+        sum(
+            abs(rc1[0] - rc2[0]) + abs(rc1[1] - rc2[1])
+            for rc1, rc2 in combinations(g2, 2)
+        )
+    )
+
+    return p1, p2
+
+
+if __name__ == "__main__":
+    with open("./input/11.txt", "r") as f:
+        inp = f.read().strip()
+
+    inp = presolve(inp)
+
+    a = part_1(inp)
+    b = part_2(inp)
+
+    assert a == 9370588
+    assert b == 746207878188