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| #pragma GCC optimize(2)
#include <bits/stdc++.h>
using namespace std;
using LL = long long;
using PII = pair<int,int>;
using PLL = pair<LL, LL>;
const int INF = 1e9;
const int MXN = 0;
const int MXV = 505;
#define MP make_pair
#define PB push_back
#define F first
#define S second
#define FOR(i, L, R) for(int i = L; i != (int)R; ++i)
#define FORD(i, L, R) for(int i = L; i != (int)R; --i)
#define IOS cin.tie(nullptr); cout.tie(nullptr); ios_base::sync_with_stdio(false);
template <typename T>
struct Dinic
{
int n, s, t, level[MXV], now[MXV];
struct Edge
{
int v;
T rf;
int re;
};
vector<Edge> e[MXV];
void init(int _n, int _s, int _t)
{
n = _n;
s = _s;
t = _t;
for (int i = 0; i <= n; i++)
{
e[i].clear();
}
}
void add_edge(int u, int v, T f)
{
e[u].push_back({v, f, (int)e[v].size()});
e[v].push_back({u, f, (int)e[u].size() - 1});
}
bool bfs()
{
fill(level, level + n + 1, -1);
queue<int> q;
q.push(s);
level[s] = 0;
while (!q.empty())
{
int u = q.front();
q.pop();
for (auto it : e[u])
{
if (it.rf > 0 && level[it.v] == -1)
{
level[it.v] = level[u] + 1;
q.push(it.v);
}
}
}
return level[t] != -1;
}
T dfs(int u, T limit)
{
if (u == t)
return limit;
int res = 0;
while (now[u] < (int)e[u].size())
{
Edge &it = e[u][now[u]];
if (it.rf > 0 && level[it.v] == level[u] + 1)
{
T f = dfs(it.v, min(limit, it.rf));
res += f;
limit -= f;
it.rf -= f;
e[it.v][it.re].rf += f;
if (limit == 0)
{
return res;
}
}
else
{
++now[u];
}
}
if (!res)
{
level[u] = -1;
}
return res;
}
T flow(T res = 0)
{
while (bfs())
{
T tmp;
memset(now, 0, sizeof(now));
do{
tmp = dfs(s, INF);
res += tmp;
}while(tmp);
}
return res;
}
void find_minimum_cut()
{
FOR(i, 1, n + 1)if(level[i] != -1)
{
for(auto edge: e[i])
{
if(level[edge.v] == -1 && edge.rf == 0)
{
cout << i << ' ' << edge.v << '\n';
}
}
}
}
};
int main()
{
IOS;
int m, n;
Dinic<LL> dinic;
bool delimiter = false;
while(cin >> m >> n, m || n)
{
if(delimiter)
{
cout << '\n';
}
delimiter = true;
dinic.init(m, 1, 2);
int x, y;
LL c;
FOR(i, 0, n)
{
cin >> x >> y >> c;
dinic.add_edge(x, y, c);
}
dinic.flow();
dinic.find_minimum_cut();
}
}
|
