Breadth first search stuck in infinite loop

Question

I am trying to implement breadth first search algorithm but due to some reasons it is getting stuck in infinite loop.

I have tried debugging it by outputting various values but still no success.

My Bfs Code


    int s=0;
    bool vis[n];
    int dist[n];

    for(int i=0;i<n;i++){
        vis[i]=false;
        dist[i]=INT_MAX;
    }

    dist[s]=0;
    vis[s]=true;
    q_push(s);



    while(!q_isEmpty()){
        int u = queu[0];
        for(int v=0;v<n;v++){
            if(adjMat[u][v]==1){
                if(vis[v]==false){
                    vis[v] == true;
                    dist[v]=dist[u]+1;
                    q_push(v);
                    cout<<v;
                }
            }
        }

        q_pop();


    }

My queue is globally declared its code

vector <int> queu;

void q_push(int d){
    queu.insert(queu.end(),d);

}

void q_pop(){
    queu.erase(queu.begin());
}

bool q_isEmpty(){
    return queu.empty();
}

I take adjacency matrix as input its code.

int n;
cin>>n;
for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
        int temp;
        cin>>temp;
        adjMat[i][j]=temp;
    }
}

Did you know there is a [std::queue](https://en.cppreference.com/w/cpp/container/queue)? Also please post a [mcve]. — PaulMcKenzie, Oct 23 '19 at 20:31
@Imretardedbut -- `bool vis[n];` -- If `n` is not a constant, then that code is not valid C++. Use `std::vector` instead. — PaulMcKenzie, Oct 23 '19 at 20:33

score 0 · Accepted Answer · answered Oct 23 '19 at 20:33

0

Change this:

vis[v] == true;

to this:

vis[v] = true;

since you want to mark the adjacent node v as visited, by assigning it the value true - you mistakenly used the comparison operator instead of the assignment operator, so you keep and keep visiting nodes that you already traversed, again and again, going into an infinite loop..

PS: Not the cause of the infinite loop, but as @PaulMcKenzie commented, you could/should use an std::queue.

answered Oct 23 '19 at 20:33

gsamaras

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Thanks for the help. I was trying to implement everything from scratch for better understanding – Im retarded but Oct 23 '19 at 20:37
No problem @Imretardedbut, practice is good! :) If my answer solved your issue, you can accept it if you want. – gsamaras Oct 23 '19 at 20:38

Breadth first search stuck in infinite loop

1 Answers1