Cod sursa(job #3336638)

Utilizator CalinHanguCalinHangu CalinHangu Data 25 ianuarie 2026 02:45:03
Problema Flux maxim Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 2.82 kb
#include <iostream>
#include <vector>
#include <queue>
#define pii pair<int, int>

using namespace std;

const int NMAX = 1005;
const char nl = '\n';
const int INF = 1e9 + 7;

vector<int> graph[NMAX];
vector<int> rev_graph[NMAX];
long long flow[NMAX][NMAX]; // fluxul actual pe arce
long long capacity[NMAX][NMAX]; // capacitatea pe arce
int father[NMAX]; // pentru a putea parcurge drumul inapoi
int visited[NMAX];

bool bfs(int n) {
    for(int i = 1; i <= n; ++i) {
        father[i] = 0;
        visited[i] = 0;
    }

    queue<int> q;

    int source = 1;
    visited[source] = 1;
    q.push(source);

    while(!q.empty()) {
        auto curr_node = q.front();
        q.pop();

        for(auto neigh: graph[curr_node]) {
            if(visited[neigh] == 0 && capacity[curr_node][neigh] - flow[curr_node][neigh] > 0) {
                father[neigh] = curr_node; // tata pozitiv => arc direct
                visited[neigh] = 1;
                q.push(neigh);

                if(neigh == n) {
                    return true;
                }
            }
        }

        for(auto neigh: rev_graph[curr_node]) {
            if(visited[neigh] == 0 && flow[neigh][curr_node] > 0) {
                father[neigh] = -curr_node; // tata negativ => arc invers
                visited[neigh] = 1;
                q.push(neigh);

                if(neigh == n) {
                    return true;
                }
            }
        }
    }

    return false;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    freopen("maxflow.in", "r", stdin);
    freopen("maxflow.out", "w", stdout);

    int n, m;
    cin >> n >> m;

    for(int i = 0; i < m; ++i) {
        int u, v, w;
        cin >> u >> v >> w;

        graph[u].push_back(v);
        rev_graph[v].push_back(u);
        capacity[u][v] = w;
    }

    long long max_flow = 0;

    while(bfs(n)) {
        int node = n;
        long long residual_capacity = INF;

        while(node != 1) {
            if(father[node] > 0) {
                residual_capacity = min(residual_capacity, capacity[father[node]][node] - flow[father[node]][node]);
                node = father[node];
            } else {
                residual_capacity = min(residual_capacity, flow[node][-father[node]]);
                node = -father[node];
            }
        }

        node = n;

        while(node != 1) {
            if(father[node] > 0) {
                flow[father[node]][node] += residual_capacity;
                node = father[node];
            } else {
                flow[node][-father[node]] -= residual_capacity;
                node = -father[node];
            }
        }

        max_flow += residual_capacity;
    }

    cout << max_flow << nl;
    return 0;
}