Create 01 - BFS Approach.cpp

Author: JawadSher

23 - Graph Data Structure Problems/07 - Undirected Graph Cycle | BFS - DFS/01 - BFS Approach.cpp

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+class Solution {
+  public:
+    bool isCycleBFS(int src, unordered_map<int, bool> &visited, vector<vector<int>>& adj){
+        unordered_map<int, int> parent;
+        
+        parent[src] = -1;
+        visited[src] = true;
+        queue<int> q;
+        q.push(src);
+        
+        while(!q.empty()){
+            int front = q.front();
+            q.pop();
+            
+            for(auto neighbour : adj[front]){
+                if(visited[neighbour] == true && neighbour != parent[front]) return true;
+                else if(!visited[neighbour]){
+                    q.push(neighbour);
+                    visited[neighbour] = true;
+                    parent[neighbour] = front;
+                }
+            }
+        }
+        
+        return false;
+    }
+    
+    bool isCycle(vector<vector<int>>& adj) {
+        int n = adj.size();
+        
+        unordered_map<int, bool> visited;
+        for(int i = 0; i < n; i++){
+            if(!visited[i]){
+                bool ans = isCycleBFS(i, visited, adj);
+                if(ans == 1) return true;
+            }
+        }
+        
+        
+        return false;
+    }
+};