day 5 cleanup

day05/sol.py

@@ -25,6 +25,7 @@ def solve(file):
                     return False
         return True
 
+    # part 1
     t = 0
     invalid = []
     for pages in updates:
@@ -35,13 +36,20 @@ def solve(file):
             invalid.append(pages)
     print(t)
 
+    # part 2: select applicable rules and form a graph
+    # find the root node
+    # do a topological sort by doing a DFS of the graph
     t = 0
     for pages in invalid:
+        # select rules
         rules2 = [(p,g) for p,g in rules if p in pages and g in pages]
         #print(pages, rules2)
+
+        # find root node
         S = set(p for p,g in rules2)
         E = set(g for p,g in rules2)
         top = next(iter(S-E))
+
         # topological sort
         l = []
         seen = set()
@@ -54,53 +62,16 @@ def solve(file):
             l.append(node)
         visit(top)
         l.reverse()
+
+        # sanity check
+        assert len(l) == len(pages)
+        assert isvalid(l)
         print(l)
+
+        # add middle number to total
         t += int(l[len(l)//2])
     print(t)
 
-    # failed attempt: establish a total order by iterating the graph
-    # to a fix point and then using it to sort the list.
-    # failed because the graph is cyclic
-    """
-    less = {p:set() for p,g in rules}
-    for p,g in rules:
-        less[p].add(g)
 
-    print("less")
-    for p in less:
-        print(p,less[p])
-
-    done = False
-    while not done:
-        done = True
-        for p in less:
-            for g in list(less[p]):
-                if g in less:
-                    e = less[g] - less[p]
-                    if e:
-                        less[p] |= e
-                        done = False       
-    print("less2")
-    for p in less:
-        print(p,less[p])
-
-    def compare(a,b):
-        if a == b:
-            return 0
-        if a in less and b in less[a]:
-            return -1
-        return 1
-
-    t = 0
-    for pages in invalid:
-        pages.sort(key = functools.cmp_to_key(compare))
-        print(pages)
-        assert(isvalid(pages))
-        t += int(pages[len(pages)//2])
-    print(t)
-    """
-
-        
-            
 solve(open("sample1.in"))
 solve(open("input"))