BZOJ 1927 星际竞速

每个点可以由a[i],走边 两种形式到达。于是拆点，在右边直连汇点，和连图中的边，从而表达了“或”的含义。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
#include<algorithm>
#define maxv 1650
#define maxe 500500
#define inf 2000000000
using namespace std;
int n,m,a[maxv],x,y,z,nume=1,g[maxv],s,t;
int dis[maxv],prev[maxv],pree[maxv];
bool vis[maxv];
queue <int> q;
struct edge
{
    int v,f,c,nxt;
}e[maxe];
void addedge(int u,int v,int f,int c)
{
    e[++nume].v=v;e[nume].f=f;e[nume].c=c;e[nume].nxt=g[u];g[u]=nume;
    e[++nume].v=u;e[nume].f=0;e[nume].c=-c;e[nume].nxt=g[v];g[v]=nume;
}
bool spfa()
{
    for (int i=s;i<=t;i++) {vis[i]=false;dis[i]=inf;prev[i]=pree[i]=-1;}
    vis[s]=true;dis[s]=0;q.push(s);
    while (!q.empty())
    {
        int head=q.front();q.pop();vis[head]=false;
        for (int i=g[head];i;i=e[i].nxt)
        {
            int v=e[i].v;
            if ((e[i].f>0) && (dis[v]>dis[head]+e[i].c))
            {
                dis[v]=dis[head]+e[i].c;
                 prev[v]=head;pree[v]=i;
                if (!vis[v]) {vis[v]=true;q.push(v);}
            }
        }
    }
    if (dis[t]==inf) return false;
    return true;
}
int dinic()
{
    int u=t,dt=inf;
    while (u!=s)
    {
        dt=min(dt,e[pree[u]].f);
        u=prev[u];
    }
    u=t;
    while (u!=s)
    {
        e[pree[u]].f-=dt;e[pree[u]^1].f+=dt;
        u=prev[u];
    }
    return dis[t]*dt;
}
int main()
{
    scanf("%d%d",&n,&m);s=0;t=2*n+1;
    for (int i=1;i<=n;i++)
    {
        scanf("%d",&a[i]);
        addedge(s,i,1,0);
        addedge(i+n,t,1,0);
        addedge(s,i+n,1,a[i]);
    }
    for (int i=1;i<=m;i++)
    {
        scanf("%d%d%d",&x,&y,&z);
        if (x>y) swap(x,y);
        addedge(x,y+n,1,z);
    }
    int min_cost=0;
    while (spfa())
        min_cost+=dinic();
    printf("%d\n",min_cost);
    return 0;
}