Cod sursa(job #1118874)

Utilizator rares96cheseliRares Cheseli rares96cheseli Data 24 februarie 2014 13:40:45
Problema Flux maxim Scor 100
Compilator cpp Status done
Runda Arhiva educationala Marime 1.66 kb
#include <fstream>
#include <vector>
#include <queue>
#define pb push_back
using namespace std;
ifstream f("maxflow.in");
ofstream g("maxflow.out");

int N, M, flow[1002][1002], cap[1002][1002], x, y, c, maxflow, source, sink, prec[1002];
vector < int > G[1002];
queue < int > Q;

bool bfs(int source)
{
    for (int i=1; i<=N; ++i)
        prec[i]=0; prec[source]=source;
    Q.push(source);
    while (Q.size())
    {
        int nod=Q.front(); Q.pop();
        if (nod==sink) continue;
        vector <int>::iterator it=G[nod].begin();
        for (; it!=G[nod].end(); ++it)
            if (!prec[*it] && cap[nod][*it]>flow[nod][*it])
                prec[*it]=nod, Q.push(*it);
    }
    return prec[sink]>0;
}

void flux(int source)
{
    while ( bfs(source) )
    {
        vector<int>::iterator it=G[sink].begin();
        for (; it!=G[sink].end(); ++it)
            if (prec[*it] && cap[*it][sink]>flow[*it][sink])
            {
                int minim=(1<<30);
                prec[sink]=*it;
                for (int x=sink; x!=source; x=prec[x])
                    if (cap[prec[x]][x]-flow[prec[x]][x]<minim)
                        minim=cap[prec[x]][x]-flow[prec[x]][x];

                if (minim>0)
                {
                    maxflow+=minim;
                    for (int x=sink; x!=source; x=prec[x])
                        flow[prec[x]][x]+=minim, flow[x][prec[x]]-=minim;
                }
            }
    }
}

int main()
{
    f>>N>>M; source=1; sink=N;
    for (int i=1; i<=M; ++i)
        f>>x>>y>>c, G[x].pb(y), G[y].pb(x), cap[x][y]+=c;

    flux(source);
    g<<maxflow<<'\n';
    return 0;
}