C++ vd::begin方法代码示例

	double Sum( vd v)
	{
		vd::iterator it;
		double sum = 0.0;

		for(it = v.begin(); it < v.end(); ++it)
			sum += *it;

		return(sum);
	}

	double SumSquaredDifferences( vd v, double avg)
	{
		vd::iterator it;
		double sumSq = 0.0;

		for(it = v.begin(); it < v.end(); ++it)
			sumSq += pow(*it - avg,2.0);

		return( sumSq );
	}

	double average( vd v)
	{
		vd::iterator it;
		double sum = 0.0;

		if ( v.size() == 0) return(0.0);

		for(it = v.begin(); it < v.end(); ++it)
			sum += *it;

		return(sum/v.size());
	}

//shortest path from a node n to every other node: 
//this is for any graphs even ones that have negative weights -- can detect negative cycles
//for every vertex, relax E times
//as an optimization we use a queue to store vertices that changed
//and relax paths only from that queue
//to detect negative loops can check if node n gets updated on any the n-th iteration
int BellmanFordMoore(const graphtp & g, vd & D, int src)     
{
    int comparisons = 0;
    vi visited(g.size());
    std::vector<edge> P(g.size()); //parent node for node e.to is e.from

    for(vd::iterator it = D.begin(); it != D.end(); ++it) 
        *it = INFINITY;
    D[src] = 0;

    si lastupdated;

    //keep a queue (set) of vertices (nodes) that were updated last time around
    //do the relaxation V times 
    for(size_t i = 0; i < g.size(); i++) {
        lastupdated.insert(i);
    }


    //without optimization loop would be: for(int i = 0; i < g.size(); i++) 
    size_t counter = 0;
    while(!lastupdated.empty()) {
        counter++;
        si newlast;
        //visit and relax all edges (two for loopxs needed to visit all edges)
        for(si::iterator jt = lastupdated.begin();jt != lastupdated.end(); jt++)
        {
            int v = *jt;
            out("next to work on is %d\n", v);
            for(ve::const_iterator it = g[v].begin(); it != g[v].end(); ++it)
            {
                float dist = D[v] + it->weight;
                assert(v == it->from && "not the same node");
                if(D[it->to] > dist) { //this is the relaxation step
                    out("counter %d, it->to %d\n", counter, it->to);
                    if(counter >= g.size()) { 
                        //we should not update a node in a stage greater than sz
                        printf("negative cycles exists distance %d to %d is %f\n", v, it->to, dist);
                        //need to trace back from P[v]
                        //printSP(P, it->to, v);
                        printSP(P, v, it->to);
                        printf("\n");
                        return -1;
                    }
                    D[it->to] = dist;
                    P[it->to] = *it;
                    newlast.insert(it->to); //track which changed
                    out("new distance %d to %d is %f\n", v, it->to, dist);
                }
            }
        }
        lastupdated = newlast;
    }

    for(size_t i = 0; i < D.size(); i++) {
        printf("%d -> %d sp=%.2f ", src, i, D[i]);
        printSP(P, i, src);
        printf("\n");
    }
    out("comparisons %d\n", comparisons);
    return 0;
}