Cod sursa(job #2955895)

Utilizator moise_alexandruMoise Alexandru moise_alexandru Data 18 decembrie 2022 03:28:23
Problema Flux maxim Scor 40
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 2.5 kb
#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
using namespace std;
ifstream in("maxflow.in");
ofstream out("maxflow.out");
const int maxn = 1005;
int dist[maxn];

struct muchie {
    int nod;
    int vec;
    int flux;
    int cap;
};

vector <muchie> v[maxn];
int tata[maxn];
queue <int> q;
int n;

bool bfs()
{
    for(int i = 1; i <= n; i++)
    {
        dist[i] = (1 << 30);
        tata[i] = 0;
    }
    dist[1] = 0;
    q.push(1);
    while(!q.empty())
    {
        int nod = q.front();
        q.pop();
        for(auto it : v[nod])
        {
            if(dist[it.vec] > dist[nod] + 1 && it.flux < it.cap) /// pot trimite flux pe aici
            {
                dist[it.vec] = dist[nod] + 1;
                tata[it.vec] = nod;
                q.push(it.vec);
            }
        }
    }
    if(dist[n] != (1 << 30))
        return 1;
    return 0;
}

int main()
{
    int m;
    in >> n >> m;
    for(int i = 1; i <= m; i++)
    {
        int x, y, cap;
        in >> x >> y >> cap;
        v[x].push_back({x, y, 0, cap});
        v[y].push_back({y, x, 0, 0});
    }
    while(bfs()) /// cat timp gasesc un drum de la 1 la n
    {
        int act = n;
        vector <pair <int, int> > drum;
        while(tata[act])
        {
            drum.push_back(make_pair(tata[act], act));
            act = tata[act];
        }
        int posibil = (1 << 30); /// fluxul maxim pe care il pot trimite pe drumul gasit
        for(auto m : drum) /// m.first - m.second e muchia pe care o caut
        {
            int x = m.first;
            int y = m.second;
            for(auto it : v[x])
                if(it.vec == y) /// am gasit muchia
                    posibil = min(posibil, it.cap - it.flux);
        }
        for(auto m : drum) /// fac acelasi lucru dar acum scad fluxul pe care il bag din toate muchiile
        {
            int x = m.first;
            int y = m.second;
            for(int i = 0; i < v[x].size(); i++) /// gasesc muchia (x, y) si adun fluxul bagat
                if(v[x][i].vec == y)
                    v[x][i].flux += posibil;
            for(int i = 0; i < v[y].size(); i++)
                if(v[y][i].vec == x)
                    v[y][i].flux -= posibil; /// gasesc muchia (y, x) si scad fluxul bagat
        }
    }
    int total = 0;
    for(auto it : v[1]) /// ma uit cat iese din 1 ca sa aflu fluxul trimis
        total = total + it.flux;
    out << total << "\n";
    return 0;
}