BZOJ 1880: [Sdoi2009]Elaxia的路线

#include <cstring>
#include <cstdio>
#include <cctype>
#include <queue>
#define M 1000005
#define N 1505
using namespace std;
struct Edge
{
    int x,y,z;
}e[M];
int dist[2][N],D[N],nextt[M<<1],to[M<<1],head[M<<1],val[M<<1],cnt,n,m,s[3],t[3],f[N],use[M];
inline void Read(int &x)
{
    register char ch=getchar();
    for(x=0;!isdigit(ch);ch=getchar());
    for(;isdigit(ch);x=x*10+ch-‘0‘,ch=getchar());
}
inline void ins(int u,int v,int l)
{
    nextt[++cnt]=head[u];
    to[cnt]=v;
    val[cnt]=l;
    head[u]=cnt;
}
bool vis[N];
struct node
{
    int x,y;
    bool operator<(node a)const
    {
        return y>a.y;
    }
};
void dijkstra(int s,int *dis)
{
    memset(dis,0x3f,sizeof(dist[0]));
    memset(vis,0,sizeof(vis));
    dis[s]=0;
    priority_queue<node>q;
    q.push((node){s,dis[s]});
    for(node now;!q.empty();)
    {
        now=q.top();
        q.pop();
        if(vis[now.x]) continue;
        vis[now.x]=1;
        for(int i=head[now.x];i;i=nextt[i])
        {
            int v=to[i];
            if(dis[v]>dis[now.x]+val[i])
            {
                dis[v]=dis[now.x]+val[i];
                q.push((node){v,dis[v]}); 
            }
        }
    }
}
inline void swap(int &x,int &y) {int tmp=y;y=x;x=tmp;}
inline int min(int x,int y) {return x>y?y:x;}
inline int max(int x,int y) {return x>y?x:y;}
void calc(int s,int t)
{
    for(int i=1;i<=m;++i)
    {
        int x=e[i].x,y=e[i].y,z=e[i].z;
        if(min(dist[0][x],dist[0][y])+min(dist[1][x],dist[1][y])+z==dist[0][t]) use[i]++;
    }
}
int main(int argc,char *argv[])
{
    Read(n);Read(m); 
    for(int i=1;i<=2;++i) Read(s[i]),Read(t[i]);
    for(int a,b,c,i=1;i<=m;++i)
    {
        Read(a);Read(b);Read(c);
        e[i]=(Edge){a,b,c};
        ins(a,b,c);
        ins(b,a,c);
    }
    for(int i=1;i<=2;++i)
    {
        dijkstra(s[i],dist[0]);
        dijkstra(t[i],dist[1]);
        calc(s[i],t[i]);
    }
    memset(head,0,sizeof(head));
    cnt=0;
    for(int i=1;i<=m;++i)
    {
        if(use[i]==2)
        {
            int x=e[i].x,y=e[i].y,z=e[i].z;
            if(dist[0][x]>dist[0][y]) swap(x,y);
            ins(x,y,z);D[y]++;
        }
    }
    int h=0,t=0,Que[N];
    for(int i=1;i<=n;++i) if(!D[i]) Que[++t]=i;
    for(int now;h<t;)
    {
        now=Que[++h];
        for(int i=head[now];i;i=nextt[i])
        {
            int v=to[i];
            f[v]=max(f[now]+val[i],f[v]);
            D[v]--;
            if(D[v]==0) Que[++t]=v;
        }
    }
    int ans=0;
    for(int i=1;i<=n;++i) ans=max(ans,f[i]);
    printf("%d\n",ans);
    return 0;
}