# Demo entry 6631486

Submitted by anonymous on Jul 15, 2017 at 14:28
Language: C++. Code size: 2.9 kB.

```// UVa1658 Admiral
/**最小费用最大流
1 拆点法 每个点(除汇点、源点外)只能经过一次【有结点容量限制】
2 指定最大流量的值【有总流量限制】
*/
#include<cstdio>
#include<cstring>
#include<queue>
#include<vector>
#include<algorithm>
#include<cassert>
using namespace std;

const int maxn = 2000 + 10;
const int INF = 1000000000;

struct Edge {
int from, to, cap, flow, cost;
Edge(int u, int v, int c, int f, int w):from(u),to(v),cap(c),flow(f),cost(w) {}
};

struct MCMF {
int n, m;
vector<Edge> edges;
vector<int> G[maxn];
int inq[maxn];         // 是否在队列中
int d[maxn];           // Bellman-Ford
int p[maxn];           // 上一条弧
int a[maxn];           // 可改进量

void init(int n) {
this->n = n;
for(int i = 0; i < n; i++) G[i].clear();
edges.clear();
}

void AddEdge(int from, int to, int cap, int cost) {
edges.push_back(Edge(from, to, cap, 0, cost));
edges.push_back(Edge(to, from, 0, 0, -cost));
m = edges.size();
G[from].push_back(m-2);
G[to].push_back(m-1);
}

bool BellmanFord(int s, int t, int flow_limit, int& flow, int& cost) {
for(int i = 0; i < n; i++) d[i] = INF;
memset(inq, 0, sizeof(inq));
d[s] = 0; inq[s] = 1; p[s] = 0; a[s] = INF;

queue<int> Q;
Q.push(s);
while(!Q.empty()) {
int u = Q.front(); Q.pop();
inq[u] = 0;
for(int i = 0; i < G[u].size(); i++) {
Edge& e = edges[G[u][i]];
if(e.cap > e.flow && d[e.to] > d[u] + e.cost) {
d[e.to] = d[u] + e.cost;
p[e.to] = G[u][i];
a[e.to] = min(a[u], e.cap - e.flow);
if(!inq[e.to]) { Q.push(e.to); inq[e.to] = 1; }
}
}
}
if(d[t] == INF) return false;
//如果本次更新后超出指定最大流量，则只更新部分，使得结果正好等于指定最大流量
if(flow + a[t] > flow_limit) a[t] = flow_limit - flow;
flow += a[t];
cost += d[t] * a[t];
for(int u = t; u != s; u = edges[p[u]].from) {
edges[p[u]].flow += a[t];
edges[p[u]^1].flow -= a[t];
}
return true;
}

// 需要保证初始网络中没有负权圈
int MincostFlow(int s, int t, int flow_limit, int& cost) {
int flow = 0; cost = 0;
//flow<flow_limit是指明，流量小于指定最大流量的情况下，才可以继续尝试bellmanford
while(flow < flow_limit && BellmanFord(s, t, flow_limit, flow, cost));
return flow;
}

};

MCMF g;

int main() {
int n, m, a, b, c;
while(scanf("%d%d", &n, &m) == 2 && n) {
g.init(n*2-2);

// 点2~n-1拆成弧i->i'，前者编号为0~n-1，后者编号为n~2n-3
for(int i = 2; i <= n-1; i++)

while(m--) {
scanf("%d%d%d", &a, &b, &c);
// 连a'->b
if(a != 1 && a != n) a += n-2; else a--;  // 编号从0开始
b--;  // 编号从0开始