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Count Number of Connected Components [TC: O(V+E); SC: O(V+E)]
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#include <queue> | |
#include <vector> | |
#include <iostream> | |
#include <algorithm> | |
using namespace std; | |
void addEdge(vector<int> *adj, int u, int v) { | |
adj[u].push_back(v); | |
adj[v].push_back(u); | |
} | |
void BFS(vector<int> *G, int V, int s, vector<bool> &vis) { | |
queue<int> Q; | |
vis[s] = true; | |
Q.push(s); | |
while(!Q.empty()) { | |
int u = Q.front(); Q.pop(); | |
// cout << u << " "; // To print the vertices in graph G | |
for(int v: G[u]) | |
if(!vis[v]) { | |
vis[v] = true; | |
Q.push(v); | |
} | |
} | |
} | |
int BFSDisconnected(vector<int> *G, int V) { | |
int count = 0; | |
vector<bool> visited(V+1, false); | |
for(int i = 0; i < V; ++i) | |
if(!visited[i]) | |
++count, BFS(G, V, i, visited); | |
return count; | |
} | |
int main() { | |
int t; cin >> t; | |
while(t--) { | |
int vertices, edges, u, v; | |
cin >> vertices >> edges; | |
// Initialize the graph: G(V, E) -> represented as G[u][v] | |
vector<int> G[vertices]; | |
for(int i = 0; i < edges; ++i) { | |
cin >> u >> v; | |
addEdge(G, u-1, v-1); // for 0-based indexing | |
} | |
cout << BFSDisconnected(G, vertices) << "\n"; | |
} | |
return 0; | |
} |
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