day 5 part 2

day05/sol.py

@@ -35,6 +35,70 @@ def solve(file):
             invalid.append(pages)
     print(t)
 
+    t = 0
+    for pages in invalid:
+        rules2 = [(p,g) for p,g in rules if p in pages and g in pages]
+        #print(pages, rules2)
+        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()
+        def visit(node):
+            if node in seen: return
+            seen.add(node)
+            for p,g in rules2:
+                if p == node and g not in seen:
+                    visit(g)
+            l.append(node)
+        visit(top)
+        l.reverse()
+        print(l)
+        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)
+    """