Cod sursa(job #1553548)

Utilizator ArkinyStoica Alex Arkiny Data 20 decembrie 2015 00:29:57
Problema Flux maxim Scor 100
Compilator cpp Status done
Runda Arhiva educationala Marime 1.78 kb
#include<fstream>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;


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

vector<int> G[1001];
int N, M, a, b, c, i, T = 0;
int viz[1001];
int from[1001], O[1001], A[1001][1001];
int BFS(int x)
{
	queue<int> q;
	q.push(x);
	viz[x] = T + 1;
	int i;
	while (q.size())
	{
		x = q.front();

		q.pop();

		if (x == N)
		{
			return 1;
		}
		for (i = 0; i < G[x].size();++i)
			if (viz[G[x][i]] <= T && A[x][G[x][i]]>0)
			{
				q.push(G[x][i]);
				viz[G[x][i]] = T + 1;
				from[G[x][i]] = x;
			}
	}
	return 0;
}
void update(int x)
{
	for (int i = 0;i < G[x].size();++i)
	{
		if (A[G[x][i]][N] == 0 || viz[x] != T + 1)
			continue;
		int leaf = G[x][i];
		int duplicate = leaf;
		int min_flow = A[G[x][i]][N];
		for (;from[leaf];leaf = from[leaf])
			min_flow = min(min_flow, A[from[leaf]][leaf]);
		
		leaf = duplicate;
		if (A[G[x][i]][N] - min_flow >= 0)
		{
			A[G[x][i]][N] -= min_flow;
			A[N][G[x][i]] += min_flow;
		}
		else
		{
			A[G[x][i]][N] += min_flow;
			A[N][G[x][i]] -= min_flow;
		}
		for (;from[leaf];leaf = from[leaf])
		{
			if (A[from[leaf]][leaf] - min_flow >= 0)
			{
				A[from[leaf]][leaf] -= min_flow;
				A[leaf][from[leaf]] += min_flow;
			}
			else
			{
				A[from[leaf]][leaf] += min_flow;
				A[leaf][from[leaf]] -= min_flow;
			}
		}
	}
}
void Edmond()
{
	while (BFS(1))
	{
		update(N);
		++T;
	}
}



int main()
{
	in >> N >> M;
	for (i = 1; i <= M; ++i)
	{
		in >> a >> b >> c;
		G[a].push_back(b);
		A[a][b] = c;
		G[b].push_back(a);
	}
	for (i = 0; i < G[1].size(); ++i)
		O[i] = A[1][G[1][i]];
	Edmond();
	int s = 0;
	for (i = 0; i < G[1].size(); ++i)
		s += O[i] - A[1][G[1][i]];
	out << s;
	return 0;
}