bzoj 2324 营救皮卡丘

floyd预处理 ＋ 费用流

/**************************************************************
    Problem: 2324
    User: Clare
    Language: C++
    Result: Accepted
    Time:300 ms
    Memory:5408 kb
****************************************************************/
 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
using namespace std;
 
#define N 310
#define INF 0x3f3f3f3f
 
int n,m,K,S,T;
struct Edge{
    int next,to,value,cost,from;
}edge[N*N*2];
int head[N],tot=1;
int dis[N][N],d[N],pre[N];
long long Ans;
queue Q;
bool exist[N];
 
inline int read()
{
    int x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch<='9'&&ch>='0'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
 
void Addedge(int u,int v,int w,int c)
{
    tot++;edge[tot].next=head[u];edge[tot].to=v;edge[tot].from=u;
    edge[tot].value=w;edge[tot].cost=c;head[u]=tot;
    tot++;edge[tot].next=head[v];edge[tot].to=u;edge[tot].from=v;
    edge[tot].value=0;edge[tot].cost=-c;head[v]=tot;
}
 
void Pre_floyd()
{
    for(int k=0;k<=n;k++)
    {
        for(int i=0;i<=n;i++)
        {
            for(int j=0;j<=n;j++)
            {
                if(k>i&&k>j)
                    continue;
                if(dis[i][j]>dis[i][k]+dis[k][j])
                    dis[i][j]=dis[i][k]+dis[k][j];
            }
        }
    }
}
 
bool SPFA()
{
    memset(d,INF,sizeof(d));
    memset(exist,0,sizeof(exist));
    d[S]=0;exist[S]=1;
    Q.push(S);
    while(!Q.empty())
    {
        int now=Q.front();Q.pop();
        exist[now]=false;
        for(int i=head[now];i;i=edge[i].next)
        {
            int v=edge[i].to;
            if(edge[i].value>0&&d[v]>d[now]+edge[i].cost)
            {
                d[v]=d[now]+edge[i].cost;
                pre[v]=i;
                if(!exist[v])
                {
                    exist[v]=true;
                    Q.push(v);
                }
            }
        }
    }
    return !(d[T]==INF);
}
 
void DFS()
{
    int qwer=INF;
    for(int i=pre[T];i;i=pre[edge[i].from])
        qwer=min(qwer,edge[i].value);
    for(int i=pre[T];i;i=pre[edge[i].from])
    {
        edge[i].value-=qwer;
        edge[i^1].value+=qwer;
        Ans+=(long long)edge[i].cost*qwer;
    }
}
 
int main()
{
    n=read();m=read();K=read();
    S=0;T=2*n+2;
    for(int i=0;i<=n;i++)
        for(int j=0;j<=n;j++)
        {
            if(i!=j)
                dis[i][j]=INF;
        }
    for(int i=1;i<=m;i++)
    {
        int u=read(),v=read(),w=read();
        dis[u][v]=min(dis[u][v],w);
        dis[v][u]=dis[u][v];
    }
    Pre_floyd();
    for(int i=1;i<=n;i++)
    {
        Addedge(S,i+n+1,1,0);
        Addedge(i,T,1,0);
    }
    Addedge(S,n+1,K,0);
    for(int i=0;i<=n;i++)
        for(int j=i+1;j<=n;j++)
        {
            if(dis[i][j]!=INF)
                Addedge(i+n+1,j,1,dis[i][j]);
        }
    while(SPFA())
        DFS();
    cout<