Create shortest-cycle-in-a-graph.py

Author: kamyu104

Python/shortest-cycle-in-a-graph.py

@@ -0,0 +1,35 @@
+# Time:  O(n^2)
+# Space: O(n + e)
+
+# bfs
+class Solution(object):
+    def findShortestCycle(self, n, edges):
+        """
+        :type n: int
+        :type edges: List[List[int]]
+        :rtype: int
+        """
+        INF = float("inf")
+        def bfs(u):
+            dist = [float("inf")]*len(adj)
+            q = [u]
+            dist[u] = 0
+            while q:
+                new_q = []
+                for u in q:
+                    for v in adj[u]:
+                        if dist[v] == dist[u]-1:  # v == p
+                            continue
+                        if dist[v] != INF:
+                            return 1+dist[u]+dist[v]
+                        dist[v] = dist[u]+1
+                        new_q.append(v)                        
+                    q = new_q
+            return INF
+
+        adj = [[] for _ in xrange(n)]
+        for u, v in edges:
+            adj[u].append(v)
+            adj[v].append(u)
+        result = min(bfs(u) for u in xrange(n))
+        return result if result != INF else -1