Cod sursa(job #2901162)

Utilizator tibinyteCozma Tiberiu-Stefan tibinyte Data 13 mai 2022 08:48:12
Problema Flux maxim Scor 100
Compilator cpp-64 Status done
Runda Arhiva educationala Marime 2.37 kb
#include <bits/stdc++.h>
#define int long long
using namespace std;
ifstream fin("maxflow.in");
ofstream fout("maxflow.out");
struct edge{
    int a,b,flow,cap;
};
struct Dinic{
    vector<edge> edges;
    vector<vector<int>> g;
    vector<int> level;
    vector<int> next;
    int s,t;
    void build(int n , int _s , int _t){
        g.resize(n+1) , level.resize(n+1),next.resize(n+1);
        s = _s;
        t = _t;
    }
    void add_edge(int a , int b , int cap){
        int m = edges.size();
        edges.push_back({a,b,0,cap});
        edges.push_back({b,a,0,0});
        g[a].push_back(m);
        g[b].push_back(m+1);
    };
    bool bfs(){
        queue<int> q;
        q.push(s);
        level[s]= 0;
        while(!q.empty()){
            int node = q.front();
            q.pop();
            for(auto i : g[node]){
                edge x = edges[i];
                if(x.cap-x.flow < 1 || level[x.b] != -1){
                    continue;
                }
                level[x.b] = level[node]+1;
                q.push(x.b);
            }
        }
        return level[t] != -1;
    }
    int dfs(int node , int pushed){
        if(pushed==0){
            return 0;
        }
        if(node == t) {
            return pushed;
        }
        for(int& i = next[node]; i < (int)g[node].size(); ++i){
            edge x = edges[g[node][i]];
            if(x.cap-x.flow < 1 || level[x.b] != level[node]+1){
                continue;
            }
            int flow = dfs(x.b, min(pushed, x.cap-x.flow));
            if(flow==0){
                continue;
            }
            edges[g[node][i]].cap -= flow;
            edges[g[node][i]^1].cap += flow;
            return flow;
        }
        return 0;
    }
    int flow(){
        int ans = 0;
        while(true){
            fill(level.begin(),level.end(),-1);
            if(!bfs()){
                break;
            }
            fill(next.begin(),next.end(),0);
            while(int add = dfs(s,INT_MAX)){
                ans+=add;
            }
        }
        return ans;
    }
};
int32_t main()
{
    cin.tie(nullptr)->sync_with_stdio(false);
    int n,m;
    fin>>n>>m;
    Dinic G;
    G.build(n,1,n);
    for(int i=1 ;i<= m ; ++i){
        int a ,b, cap;
        fin>>a>>b>>cap;
        G.add_edge(a,b,cap);
    }
    fout<<G.flow();
}