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

Author: kamyu104

C++/shortest-cycle-in-a-graph.cpp

@@ -0,0 +1,44 @@
+// Time:  O(n^2)
+// Space: O(n + e)
+
+// bfs
+class Solution {
+public:
+    int findShortestCycle(int n, vector<vector<int>>& edges) {
+        static const int INF = numeric_limits<int>::max();
+
+        vector<vector<int>> adj(n);
+        for (const auto& e : edges) {
+            adj[e[0]].emplace_back(e[1]);
+            adj[e[1]].emplace_back(e[0]);
+        }
+        const auto& bfs = [&](int u) {
+            vector<int> dist(n, INF);
+            vector<int> q = {u};
+            dist[u] = 0;
+            while (!empty(q)) {
+                vector<int> new_q;
+                for (const auto& u : q) {
+                    for (const auto& v : adj[u]) {
+                        if (dist[v] == dist[u] - 1) {
+                            continue;
+                        }
+                        if (dist[v] != INF) {
+                            return 1 + dist[u] + dist[v];
+                        }
+                        dist[v] = dist[u] + 1;
+                        new_q.emplace_back(v);
+                    }
+                }
+                q = move(new_q);
+            }
+            return INF;
+        };
+
+        int result = INF;
+        for (int u = 0; u < n; ++u) {
+            result = min(result, bfs(u));
+        }
+        return result != INF ? result : -1;
+    }
+};