Cod sursa(job #1987567)

Utilizator MaligMamaliga cu smantana Malig Data 31 mai 2017 08:47:29
Problema Flux maxim Scor 100
Compilator cpp Status done
Runda Arhiva educationala Marime 1.92 kb
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <vector>
#include <queue>

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

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

int N,M,nrSol;
bool vis[NMax];
int pre[NMax],cap[NMax][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;

        if (!cap[x][y] && !cap[x][y]) {
            v[x].pb(y);
            v[y].pb(x);
        }
        cap[x][y] = c;
    }

    int maxFlow = 0;
    while (bfs()) {
        for (auto nxt : v[N]) {
            if (!vis[nxt] || !cap[nxt][N]) {
                continue;
            }

            int mnCap = inf, node = N;
            pre[N] = nxt;
            while (node != 1) {
                mnCap = min(mnCap,cap[pre[node]][node]);

                node = pre[node];
            }

            if (!mnCap) {
                continue;
            }

            node = N;
            while (node != 1) {
                cap[pre[node]][node] -= mnCap;
                cap[node][pre[node]] += mnCap;

                node = pre[node];
            }

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

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

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

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

        for (auto nxt : v[node]) {
            if (vis[nxt] || !cap[node][nxt]) {
                continue;
            }

            vis[nxt] = true;
            pre[nxt] = node;
            Q.push(nxt);
        }
    }

    return reachedN;
}