Graph BFS Traversal - C++

Question

Given an undirected and disconnected graph G(V, E), print its BFS traversal. Here you need to consider that you need to print BFS path starting from vertex 0 only. V is the number of vertices present in graph G and vertices are numbered from 0 to V-1. E is the number of edges present in graph G. Note : 1. Take graph input in the adjacency matrix. 2. Handle for Disconnected Graphs as well Input Format : Line 1: Two Integers V and E (separated by space) Next 'E' lines, each have two space-separated integers, 'a' and 'b', denoting that there exists an edge between Vertex 'a' and Vertex 'b'. Output Format : BFS Traversal (separated by space) Constraints : 2 <= V <= 1000 1 <= E <= 1000 Sample Input 1: 4 4 0 1 0 3 1 2 2 3 Sample Output 1: 0 1 3 2 Please tell what is wrong in the code.

Here is the code:

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

void print(int** edges, int V, int sv, bool* visited){
    queue<int> pq;
    pq.push(sv);
    visited[sv] = true;

    while(!pq.empty()){
        int ans = pq.front();
        cout << ans << " ";
        pq.pop();

        for(int i = 0; i < V; i++){
            if(ans == i){
                continue;
            }
            if(edges[ans][i] == 1 && !visited[i]){
                pq.push(i);
                visited[i] = true;
            }
        }

    }

}   
void BFS(int** edges, int V){
    bool* visited = new bool[V];
    for(int i = 0; i < V; i++){
        visited[i] = false;
    }
    for(int i = 0; i < V; i++){
        if(!visited[i]){
            print(edges, V, i, visited);
        }
    }
    delete [] visited;
}






int main() {
    int V, E;
    cin >> V >> E;

    int**edges = new int*[V];
    for(int i = 0; i < V; i++){
        edges[i] = new int[V];
        for(int j = 0; j < V; j++){
            edges[i][j] = 0;
        }
    }
    for(int i = 0; i < E; i++){
        int f, s;
        cin >> f >> s;
        edges[f][s] == 1;
        edges[s][f] == 1;
    }



    BFS(edges, V);

    for(int i = 0; i < V; i++){
        delete [] edges[i];
    }
    delete [] edges;

  /*

       Write Your Code Here
       Complete the Rest of the Program
       You have to take input and print the output yourself

  */


}

You never read the edges, and the edges you add are all out of bounds, which has undefined behaviour. (You don't use `E` for anything. `E` is important.) — molbdnilo, May 02 '20 at 13:17
I think `pq.pop()` pops the last element of the queue and we have to pop the front element. For that you can use the `deque` data structure of the STL which has the functions `push_back()`, `pop_back()`, `push_front()` and `pop_front()`. — srt1104, May 02 '20 at 14:02

score 0 · Answer 1 · answered Dec 04 '22 at 20:30

0

I think the only problem is a tiny mistake I see in the part you read params from command line. The algorithm itself looks good. You need to use assignment operator = instead of comparison operator == when read edges:

edges[f][s] = 1;
edges[s][f] = 1;

answered Dec 04 '22 at 20:30

Oleksandr Shtykhno

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Graph BFS Traversal - C++

1 Answers1