I can't seem to get my code to run under 2 seconds. Got the right output otherwise. This loop is what's costing me most:

for (q = 0; q < nb_steps; q++) {
    for (i=0; i<n; i++) {      
        new_numb_zombies[i] = 0;
        for (k = 0; k < nb_adj[i]; k++) {
            w = adj[i][k];
            new_numb_zombies[i] += numb_zombies[w]/nb_adj[w];
        }
    }
    aux = numb_zombies;
    numb_zombies = new_numb_zombies;
    new_numb_zombies = aux;
}

Any idea on how I could speed this up ?