C++

Forum

 
BFS cycle detection using selected nodes as input

tristanbox09 (13)
Hello guys, I am trying to use BFS to detect if a cycle is formed in the graph. I want to see if a cycle is detected by inputting selected nodes and seeing if these nodes are connected within the graph. I am currently running into an issue where if I run (0,3) --> This shouldnt be a cycle but it prints "Yes" thinking it is because of my isCyclicDisconnected it returns true when it shouldnt. Any help is much appreciated!!

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
 
// C++ program to detect cycle
// in an undirected graph
// using BFS.
#include <iostream>
#include <vector>
#include <queue>
#include <algorithm>
using namespace std;

void addEdge(vector<int> adj[], int u, int v)
{
    adj[u].push_back(v);
    adj[v].push_back(u);
}

bool isCyclicConntected(vector<int> adj[], int s, int V, vector<bool>& visited, vector<int>& bucket)
{
    // Set parent vertex for every vertex as -1.
    vector<int> parent(V, -1);

    // Create a queue for BFS
    queue<int> q;

    // Mark the current node as
    // visited and enqueue it
    visited[s] = true;
    q.push(s);
    

    while (!q.empty()) {

        // Dequeue a vertex from queue and print it
        int u = q.front();
        q.pop();

        // Get all adjacent vertices of the dequeued
        // vertex u. If a adjacent has not been visited,
        // then mark it visited and enqueue it. We also
        // mark parent so that parent is not considered
        // for cycle.
        for (auto v : adj[u])
        {
            cout << v;
            if (find(bucket.begin(), bucket.end(), v) != bucket.end()){
                
                if (!visited[v])
                {
                    visited[v] = true;
                    q.push(v);
                    parent[v] = u;
                }
                else if (parent[u] != v)
                    return true;
                
            }
        }
        
    }
    return false;
}

bool isCyclicDisconntected(vector<int> adj[], int V, vector<int>& bucket)
{
    // Mark all the vertices as not visited
    vector<bool> visited(V, false);

    for (int i = 0; i < V; i++)
        if (!visited[i] && isCyclicConntected(adj, i, V, visited, bucket))
            return true;
    return false;
}

// Driver program to test methods of graph class
int main()
{
    int const V = 4;
    vector<int> adj[V];
    addEdge(adj, 0, 1);
    addEdge(adj, 1, 2);
    addEdge(adj, 2, 0);
    addEdge(adj, 2, 3);

    vector<int> bucket;
    bucket.push_back(0);
    bucket.push_back(3);
    if (isCyclicDisconntected(adj, V, bucket))
        cout << "Yes";
    else
        cout << "No";

    return 0;
}
lastchance (6980)
What is the problem?

0 and 3 aren't cyclically connected, so isCyclicDisconnected() should return true ... so your program correctly states "Yes".

There are no adjacency links between 0 and 3 so line 44 ensures that nothing will ever get enqueued.
Topic archived. No new replies allowed.