2019 day6

2019/day6/day6.py

@@ -0,0 +1,46 @@
+from collections import defaultdict
+
+
+def path(graph, start, goal):
+    path = []
+    node = start
+    while node != goal:
+        node = graph[node]
+        path.append(node)
+    return path
+
+
+def find_first_common(x, y):
+    "returns the indices i and j of the first common element of x and y"
+    for i, xx in enumerate(x):
+        for j, yy in enumerate(y):
+            if xx == yy:
+                return i, j
+
+
+def main(inp):
+    graph = {}
+    for l in inp:
+        left, right = l.rstrip().split(")")
+        graph[right] = left
+    
+    total = 0
+    for node, child in graph.items():
+        cnt = 1
+        while child != "COM":
+            child = graph[child]
+            cnt += 1
+        total += cnt
+    print("Part 1: ", total)
+
+    p1 = path(graph, "YOU", "COM")
+    p2 = path(graph, "SAN", "COM")
+    a, b = find_first_common(p1, p2)
+    total_path = p1[:a] + p2[b::-1]  # p1 + p2 - p1 n p2
+    print("Part 2: ", len(total_path) - 1)
+
+
+if __name__ == "__main__":
+    import fileinput
+    main(fileinput.input())
+