UVa 1658 Admiral(最小费用最大流)

 

拆点费用流

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#include<cstdio>

#include<cstring>

#include<algorithm>

#include<iostream>

#include<queue>

#include<vector>

 

#define rep(i,n) for(int i=0;i<n;++i)

#define clr(x,c) memset(x,c,sizeof(x))

 

using namespace std;

 

const int maxn=2000+5;

const int inf=0x3f3f3f3f;

 

struct Edge {

int from,to,cap,flow,cost;

};

 

struct mcmf {

bool inq[maxn];

int d[maxn];

int a[maxn];

int p[maxn];

int n,s,t;

vector<int> g[maxn];

vector<Edge> edges;

void init(int n) {

this->n=n;

rep(i,n) g[i].clear();

edges.clear();

}

void addEdge(int u,int v,int cap,int cost) {

edges.push_back( (Edge) {u,v,cap,0,cost} );

edges.push_back( (Edge) {v,u,0,0,-cost} );

g[u].push_back(edges.size()-2);

g[v].push_back(edges.size()-1);

}

bool spfa(int &flow,int &cost) {

clr(d,inf); clr(inq,0);

d[s]=0; inq[s]=1; p[s]=0; a[s]=inf;

queue<int> q;

q.push(s);

while(!q.empty()) {

int x=q.front(); q.pop();

inq[x]=0;

rep(i,g[x].size()) {

Edge &e=edges[g[x][i]];

if(d[e.to]>d[x]+e.cost && e.cap>e.flow) {

d[e.to]=d[x]+e.cost;

p[e.to]=g[x][i];

a[e.to]=min(a[x],e.cap-e.flow);

if(!inq[e.to]) { q.push(e.to); inq[e.to]=1; }

}

}

}

if(d[t]==inf) return false;

flow+=a[t];

cost+=d[t]*a[t];

int x=t;

while(x!=s) {

edges[p[x]].flow+=a[t];

edges[p[x]^1].flow-=a[t];

x=edges[p[x]].from;

}

return true;

}

int minCost(int s,int t) {

this->s=s; this->t=t;

int flow=0,cost=0;

while(spfa(flow,cost));

return cost;

}

} g;

  

int main()

{

// freopen("test.in","r",stdin);

// freopen("test.out","w",stdout);

int n,m;

while(scanf("%d%d",&n,&m)==2) {

g.init(n*2+1);

int a,b,c;

while(m--) {

scanf("%d%d%d",&a,&b,&c);

if(a>1 && a<n) a+=n;

g.addEdge(a,b,1,c);

}

for(int i=2;i<n;++i) g.addEdge(i,i+n,1,0);

g.addEdge(0,1,2,0); g.addEdge(n,n*2,2,0);

printf("%d\n",g.minCost(0,n*2));

}

return 0;

}

 

 

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