Create 1192.Critical-Connections-in-a-Network.cpp

DFS/1192.Critical-Connections-in-a-Network/1192.Critical-Connections-in-a-Network.cpp

@@ -0,0 +1,59 @@
+class Solution {
+    vector<vector<int>>rets;
+    vector<vector<int>>next;
+    int time = 0;
+public:
+    vector<vector<int>> criticalConnections(int n, vector<vector<int>>& connections) 
+    {
+        next.resize(n);
+        for (auto x:connections)
+        {
+            next[x[0]].push_back(x[1]);
+            next[x[1]].push_back(x[0]);
+        }
+
+        vector<bool>visited(n);
+        vector<int>dfn(n,0);
+        vector<int>low(n,0);
+        vector<int>parent(n,-1);
+
+        for (int i = 0; i < n; i++) 
+        {            
+            if (visited[i] == false) 
+                DFS(i, visited, dfn, low, parent); 
+        }
+
+        return rets;
+    }
+
+
+    void DFS(int u, vector<bool>&visited, vector<int>&dfn, vector<int>&low, vector<int>&parent) 
+    {  
+        visited[u] = true; 
+
+        dfn[u] = low[u] = ++time; 
+
+        for (int v : next[u]) 
+        { 
+            if (v == parent[u])
+                continue;
+
+            if (!visited[v])
+            { 
+                parent[v] = u; 
+                DFS(v, visited, dfn, low, parent); 
+
+                if (low[v] > dfn[u]) rets.push_back({v,u}); // critical edge
+
+                // if(low[v] >= dfn[u]), then u is a critical vertex
+
+                low[u]  = min(low[u], low[v]); 
+            }   
+            else
+            {                
+                low[u]  = min(low[u], dfn[v]); 
+            }
+        } 
+    } 
+
+};