Cod sursa(job #1965812)

Utilizator MaligMamaliga cu smantana Malig Data 14 aprilie 2017 17:03:09
Problema Flux maxim Scor 100
Compilator cpp Status done
Runda Arhiva educationala Marime 1.91 kb
#include <iostream>
#include <fstream>
#include <queue>
#include <vector>

using namespace std;
ifstream in("maxflow.in");
ofstream out("maxflow.out");

#define pb push_back
const int NMax = 1e3 + 5;
const int MMax = 5e3 + 5;
const int inf = 1e9 + 5;

int N,M;
int cap[NMax][NMax],dad[NMax];
bool viz[NMax];
vector<int> v[NMax];

bool bfs();

int main() {
    in>>N>>M;
    for (int i=1;i<=M;++i) {
        int x,y,c;
        in>>x>>y>>c;

        cap[x][y] = c;
        //cap[y][x] = 0; // nope
        v[x].pb(y);
        v[y].pb(x);
    }

    int mxFlow = 0;
    while (bfs()) {

        for (int k=0;k < (int)v[N].size();++k) {
            int pre = v[N][k];
            if (!viz[pre] || !cap[pre][N]) {
                continue;
            }

            dad[N] = pre;
            int mnCap = inf, nod = N;
            while (nod != 1) {
                mnCap = min(mnCap,cap[dad[nod]][nod]);
                nod = dad[nod];
            }

            nod = N;
            while (nod != 1) {
                cap[dad[nod]][nod] -= mnCap;
                cap[nod][dad[nod]] += mnCap;
                nod = dad[nod];
            }

            mxFlow += mnCap;
        }
    }
    out<<mxFlow<<'\n';

    in.close();out.close();
    return 0;
}

bool bfs() {
    for (int i=1;i<=N;++i) {
        viz[i] = false;
    }

    queue<int> Q;
    viz[1] = true;
    Q.push(1);
    bool reachedN = false;
    while (Q.size()) {
        int nod = Q.front();
        Q.pop();
        if (nod == N) {
            reachedN = true;
            continue;
        }

        for (int k=0;k < (int)v[nod].size();++k) {
            int next = v[nod][k];
            if (viz[next] || !cap[nod][next]) {
                continue;
            }

            dad[next] = nod;
            viz[next] = true;
            Q.push(next);
        }
    }

    return reachedN;
}