Cod sursa(job #2968662)

Utilizator alisavaAlin Sava alisava Data 21 ianuarie 2023 18:38:14
Problema Flux maxim Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 2.96 kb
// C++ implementation of Dinic's Algorithm
#include <bits/stdc++.h>

using namespace std;

ifstream fin("maxflow.in");
ofstream  fout("maxflow.out");

// A structure to represent a edge between
// two vertex
struct Edge
{
    int v; // Vertex v (or "to" vertex)
    // of a directed edge u-v. "From"
    // vertex u can be obtained using
    // index in adjacent array.

    int flow; // flow of data in edge

    int C; // capacity

    int rev; // To store index of reverse
    // edge in adjacency list so that
    // we can quickly find it.
};

// Residual Graph
class Graph
{
    int V; // number of vertex
    int *level; // stores level of a node
    vector<Edge> *adj;

public:
    Graph(int V)
    {
        adj = new vector<Edge>[V];
        this->V = V;
        level = new int[V];
    }

    // add edge to the graph
    void addEdge(int u, int v, int C)
    {
        // Forward edge : 0 flow and C capacity
        Edge a{v, 0, C, (int) adj[v].size()};

        // Back edge : 0 flow and 0 capacity
        Edge b{u, 0, 0, (int) adj[u].size()};

        adj[u].push_back(a);
        adj[v].push_back(b); // reverse edge
    }

    bool BFS(int s, int t);

    int sendFlow(int s, int flow, int t, int ptr[]);

    int DinicMaxflow(int s, int t);
};

// Finds if more flow can be sent from s to t.
// Also assigns levels to nodes.
bool Graph::BFS(int s, int t)
{
    for (int i = 0; i < V; i++)
        level[i] = -1;

    level[s] = 0;

    list<int> q;
    q.push_back(s);

    vector<Edge>::iterator i;
    while (!q.empty())
    {
        int u = q.front();
        q.pop_front();
        for (auto &e: adj[u])
        {
            if (level[e.v] < 0 && e.flow < e.C)
            {
                level[e.v] = level[u] + 1;

                q.push_back(e.v);
            }
        }
    }
    return level[t] < 0 ? false : true;
}

int Graph::sendFlow(int u, int flow, int t, int start[])
{
    if (u == t)
        return flow;

    for (; start[u] < adj[u].size(); start[u]++)
    {
        Edge &e = adj[u][start[u]];

        if (level[e.v] == level[u] + 1 && e.flow < e.C)
        {
            int curr_flow = min(flow, e.C - e.flow);

            int temp_flow
                    = sendFlow(e.v, curr_flow, t, start);

            if (temp_flow > 0)
            {
                e.flow += temp_flow;

                adj[e.v][e.rev].flow -= temp_flow;
                return temp_flow;
            }
        }
    }
    //failed to find the target
    return 0;
}

int Graph::DinicMaxflow(int s, int t)
{
    if (s == t)
        return -1;

    int total = 0;

    while (BFS(s, t) == true)
    {
        int *start = new int[V + 1]{0};

        while (int flow = sendFlow(s, INT_MAX, t, start))
            total += flow;
    }

    return total;
}

int main()
{
    int n, m;
    int x, y, c;
    fin >> n >> m;
    Graph g(n);

    for (int i = 1; i <= m; i++)
    {
        fin >> x >> y >> c;
        g.addEdge(x - 1, y - 1, c);

    }
    fout << g.DinicMaxflow(0, n - 1) << "\n";

    return 0;
}