How do I find cycles in a graph using C++?

How do I find cycles in a graph using C++?

To find cycles in a graph using C++, you can use Depth First Search (DFS) or Union-Find algorithms. Which one would you like to know more about?

Can you explain how to implement DFS for cycle detection?

Sure! In DFS, you can keep track of visited nodes and the recursion stack. If you encounter a node that is already in the recursion stack, a cycle exists. Would you like a code example?

Yes, please provide a code example.

Here's a simple implementation of DFS for cycle detection in a directed graph:

#include <iostream>
#include <vector>
using namespace std;

bool dfs(int v, vector<bool> &visited, vector<bool> &recStack, vector<vector<int>> &graph) {
    visited[v] = true;
    recStack[v] = true;

    for (int neighbor : graph[v]) {
        if (!visited[neighbor] && dfs(neighbor, visited, recStack, graph))
            return true;
        else if (recStack[neighbor])
            return true;
    }
    recStack[v] = false;
    return false;
}

bool hasCycle(vector<vector<int>> &graph) {
    vector<bool> visited(graph.size(), false);
    vector<bool> recStack(graph.size(), false);
    for (int i = 0; i < graph.size(); i++) {
        if (!visited[i] && dfs(i, visited, recStack, graph))
            return true;
    }
    return false;
}

This code checks for cycles in a directed graph. Let me know if you need further clarification!

What about undirected graphs?

For undirected graphs, you can still use DFS, but you need to keep track of the parent node to avoid false positives. Would you like to see that implementation?