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Автор manikanta_01, история, 6 часов назад, По-английски

I gathered some information about how to approach bi-connected components As of my knowledge I created some information I think it was helpful and please forgive any mistakes which was found to be wrong now let's work together simple and beginner-friendly explanation of how to approach biconnected components (BCC) using a thrive approach (step-by-step guidance):


What Are Biconnected Components (BCC)?

A biconnected component in a graph is a maximal subgraph where:
1. Every pair of vertices has at least two disjoint paths connecting them.
2. The graph remains connected even after removing any single vertex within the component.

These are useful for understanding graph connectivity, articulation points, and bridges.


Approach to Find BCC

1. Basics to Learn First:

  • DFS (Depth-First Search): Learn how DFS works since we’ll rely on it heavily.
  • Discovery Time & Low Time: These values help us identify articulation points and bridges.
  • Discovery time (disc[u]): The time when a node u is first visited.
  • Low time (low[u]): The smallest discovery time reachable from node u.

2. Key Idea Behind BCC:

During a DFS, we track how low each node can "go back" in the DFS tree. Using this, we:
- Find articulation points: Vertices whose removal disconnects the graph.
- Group the graph into biconnected components using DFS back edges.


Thrive Approach (Step-by-Step Guide):

  1. Initialize Data Structures:
  • disc[]: To store discovery times of each node.
  • low[]: To store the lowest reachable discovery time from a node.
  • parent[]: To keep track of the DFS tree's parent for each node.
  • A stack to hold edges (used to extract the biconnected components).
  1. DFS to Compute Low and Disc Values:
    Perform a DFS, updating disc[u] and low[u] as follows:
  • When visiting a child v from u:
    • If v is unvisited, recursively call DFS on v.
    • After the DFS call, update low[u] = min(low[u], low[v]).
    • Check for an articulation point: If low[v] >= disc[u], u is an articulation point.
  • If v is already visited and is not the parent of u, it’s a back edge. Update low[u] = min(low[u], disc[v]).
  1. Detect Biconnected Components:
    Use a stack to track all edges traversed during DFS.
  • When low[v] >= disc[u], all edges in the stack from u to v form a BCC.
  • Pop edges from the stack and store them as a new biconnected component.
  1. Output the Components:
    Once the DFS finishes, you’ll have all the biconnected components grouped together.

Sample Code (Thrive Approach in Action):

Here’s a simple implementation in C++:

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

const int MAXN = 1000;
vector<int> adj[MAXN];
int disc[MAXN], low[MAXN], parent[MAXN];
bool visited[MAXN];
stack<pair<int, int>> edgeStack;
int timeCounter = 0;

void dfs(int u) {
    visited[u] = true;
    disc[u] = low[u] = ++timeCounter;
    int children = 0;

    for (int v : adj[u]) {
        if (!visited[v]) {
            children++;
            parent[v] = u;
            edgeStack.push({u, v}); // Push the edge to stack

            dfs(v);

            // Update low value of u
            low[u] = min(low[u], low[v]);

            // If u is an articulation point
            if ((parent[u] == -1 && children > 1) || (parent[u] != -1 && low[v] >= disc[u])) {
                cout << "BCC:";
                while (edgeStack.top() != make_pair(u, v)) {
                    cout << " (" << edgeStack.top().first << ", " << edgeStack.top().second << ")";
                    edgeStack.pop();
                }
                cout << " (" << edgeStack.top().first << ", " << edgeStack.top().second << ")\n";
                edgeStack.pop();
            }
        } else if (v != parent[u] && disc[v] < disc[u]) {
            // Back edge
            low[u] = min(low[u], disc[v]);
            edgeStack.push({u, v});
        }
    }
}

void findBCC(int n) {
    fill(visited, visited + n, false);
    fill(parent, parent + n, -1);
    timeCounter = 0;

    for (int i = 0; i < n; i++) {
        if (!visited[i]) dfs(i);
    }

    // Remaining edges form a BCC
    if (!edgeStack.empty()) {
        cout << "BCC:";
        while (!edgeStack.empty()) {
            cout << " (" << edgeStack.top().first << ", " << edgeStack.top().second << ")";
            edgeStack.pop();
        }
        cout << endl;
    }
}

int main() {
    int n, m;
    cin >> n >> m; // Number of nodes and edges
    for (int i = 0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    findBCC(n);
    return 0;
}

Tips for a Beginner-Friendly Thrive Approach:

  • Focus on articulation points and their relation to BCCs.
  • Draw small graphs and simulate the algorithm by hand.
  • Start with simpler cases (like trees or single cycles) to understand behavior.
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