add problem 1466

Author: luarss

Diff for: python/1466-reorder-routes-to-make-all-paths-lead-to-the-city-zero.py

@@ -0,0 +1,25 @@
+class Solution:
+    def minReorder(self, n: int, connections: List[List[int]]) -> int:
+        edges = {(a,b) for a, b in connections}
+        neighbors = defaultdict(list)
+        visit = set()
+        changes = 0
+
+        for a, b in connections:
+            neighbors[a].append(b)
+            neighbors[b].append(a)
+        
+        def dfs(city):
+            nonlocal changes
+
+            for neighbor in neighbors[city]:
+                if neighbor in visit:
+                    continue
+                # check if this neighbor can reach city 0
+                if (neighbor, city) not in edges:
+                    changes += 1
+                visit.add(neighbor)
+                dfs(neighbor)
+        visit.add(0)
+        dfs(0)
+        return changes