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Cod sursa(job #552486)
// http://infoarena.ro/problema/capacity
#include <fstream>
#include <vector>
#include <queue>
using namespace std;
#define maxSize 1001
#define INFINITY 0x3f3f3f3f
#define source 1
ifstream in("maxflow.in");
ofstream out("maxflow.out");
int destination,edges;
bool visit[maxSize];
int father[maxSize];
int capacity[maxSize][maxSize]; // capacitatea muchiei
int currentFlow[maxSize][maxSize];
vector<int> graph[maxSize];
bool breadthFirst();
int main() {
in >> destination >> edges;
int from,to,flow;
for(int i=1;i<=edges;i++) {
in >> from >> to >> flow;
capacity[from][to] = flow;
graph[from].push_back(to);
graph[to].push_back(from);
}
int maxFlow = 0;
vector<int>::iterator it,end;
// cat timp gasim drumuri de ameliorare
while(breadthFirst()) {
end = graph[destination].end();
// parcurgem drumurile invers de la
// nodurile vecine destinatiei la sursa
for(it=graph[destination].begin();it!=end;++it)
// daca nodul a fost vizitat si capacitatea
// muchie este diferita de fluxul actual
if(visit[*it] && capacity[*it][destination] != currentFlow[*it][destination]) {
int node = *it;
int minFlow = INFINITY;
father[destination] = node;
// calculam valoarea minima cu care putem mari
// fluxul pe acest drum, aceasta fiind valoarea
// minima cu care poate fi marit fluxul asociat
// fiecarei muchii care se afla pe drumul gasit
for(node=destination;node!=source;node=father[node])
minFlow = min(minFlow,capacity[father[node]][node] - currentFlow[father[node]][node]);
if(minFlow) {
for(node=destination;node!=source;node=father[node]) {
currentFlow[father[node]][node] += minFlow;
currentFlow[node][father[node]] -= minFlow;
}
maxFlow += minFlow;
}
}
}
out << maxFlow << "\n";
in.close();
out.close();
return (0);
}
bool breadthFirst() {
memset(visit,false,sizeof(visit));
visit[source] = true;
int node;
vector<int>::iterator it,end;
queue<int> myQueue;
myQueue.push(source);
while(!myQueue.empty()) {
node = myQueue.front();
myQueue.pop();
if(node == destination)
continue;
end = graph[node].end();
for(it=graph[node].begin();it!=end;++it)
// daca nodul nu a fost vizitat si fluxul
// asociat pana in acest moment este
// strict mai mic decat capacitatea muchiei
if(!visit[*it] && currentFlow[node][*it] < capacity[node][*it]) {
visit[*it] = true; // il marcam ca vizitat
myQueue.push(*it); // il introducem in coada
father[*it] = node; // ii retinem tatal (pentru reconstructia drumului)
}
}
// returneaza daca exista drum de ameliorare
return visit[destination];
}