Create main.cpp

Author: JawadSher

23 - Graph Data Structure Problems/18 - Articulation Point in Graph/main.cpp

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+class Solution {
+  public:
+    // Depth First Search to find articulation points
+    void DSF(int node, int parent, int& timer, vector<int>& disc, vector<int>& low, vector<int>& visited, vector<int>& AP, vector<vector<int>>& adjacencyList) {
+        visited[node] = true;  // Mark the node as visited
+        disc[node] = low[node] = timer++;  // Assign discovery time and initialize low
+        int child = 0;  // Count of children in DFS tree
+
+        // Traverse all neighbors of the current node
+        for (auto neighbour : adjacencyList[node]) {
+            if (neighbour == parent) continue;  // Skip the parent node
+
+            if (!visited[neighbour]) {  // If the neighbor is not visited
+                DSF(neighbour, node, timer, disc, low, visited, AP, adjacencyList);  // Recursively visit
+                low[node] = min(low[node], low[neighbour]);  // Update low value for the current node
+
+                // Check articulation point condition
+                if (low[neighbour] >= disc[node] && parent != -1) {
+                    if (find(AP.begin(), AP.end(), node) == AP.end()) AP.push_back(node);
+                }
+                child++;
+            } else {
+                low[node] = min(low[node], disc[neighbour]);  // Update low value if back edge exists
+            }
+        }
+
+        // Check root node condition
+        if (parent == -1 && child > 1) {
+            if (find(AP.begin(), AP.end(), node) == AP.end()) AP.push_back(node);
+        }
+    }
+
+    // Main function to find articulation points
+    vector<int> articulationPoints(int V, vector<int> adj[]) {
+        vector<int> disc(V, -1);  // Discovery times
+        vector<int> low(V, -1);   // Lowest discovery times
+        vector<int> visited(V, false);  // Visited nodes
+        vector<int> AP;  // Articulation points
+        int timer = 0;  // Timer to assign discovery times
+        vector<vector<int>> adjacencyList(V);
+
+        // Convert adjacency list
+        for (int i = 0; i < V; i++) {
+            for (auto neighbour : adj[i]) adjacencyList[i].push_back(neighbour);
+        }
+
+        // Perform DFS for all connected components
+        for (int i = 0; i < V; i++) {
+            if (!visited[i]) {
+                DSF(i, -1, timer, disc, low, visited, AP, adjacencyList);
+            }
+        }
+
+        // If no articulation points found, return {-1}
+        if (AP.empty()) AP.push_back(-1);
+        else sort(AP.begin(), AP.end());  // Sort the articulation points
+
+        return AP;
+    }
+};