DataStructure-And-Algorithms/Graph Theory/GraphIntro15.cpp at master · anagh9/DataStructure-And-Algorithms · GitHub

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//Cycle Detection In Unidirected Graph Graph Coloring Approach

#include<bits/stdc++.h>
using namespace std;


// } Driver Code Ends
/* This function is used to detect a cycle in undirected graph
*  adj[]: array of vectors to represent graph
*  V: number of vertices
*/
bool isCyclic_util(vector<int> adj[], vector<int> visited, int curr)
{
    if (visited[curr] == 2)
        return true;

    visited[curr] = 1;
    bool FLAG = false;
    for (int i = 0; i < adj[curr].size(); ++i)
    {
        if (visited[adj[curr][i]] == 1)
            visited[adj[curr][i]] = 2;
        else
        {
            FLAG = isCyclic_util(adj, visited, adj[curr][i]);
            if (FLAG == true)
                return true;
        }
    }
    return false;
}

bool isCyclic(vector<int> adj[], int V)
{
    vector<int> visited(V, 0);
    bool FLAG = false;
    for (int i = 0; i < V; ++i)
    {
        visited[i] = 1;
        for (int j = 0; j < adj[i].size(); ++j)
        {
            FLAG = isCyclic_util(adj, visited, adj[i][j]);
            if (FLAG == true)
                return true;
        }
        visited[i] = 0;
    }
    return false;
}

// { Driver Code Starts.

int main()
{
    int T;
    cin >> T;
    while (T--)
    {
        int V, E;
        cin >> V >> E;

        // array of vectors to represent graph
        vector<int> adj[V];

        int u, v;
        for (int i = 0; i < E; i++)
        {
            cin >> u >> v;

            // adding edge to the graph
            adj[u].push_back(v);
            adj[v].push_back(u);
        }

        cout << isCyclic(adj, V) << endl;

    }
}
// } Driver Code Ends