【BZOJ】【P1880】【Sdoi2009】【Elaxia的路线】【dijk】

传送门:http://www.lydsy.com/JudgeOnline/problem.php?id=1880

周末写了一周末的震波……还没调出来= = 、

换道题写……

最短路没的说,把可行的边定向跑dag图上最长路

用了久违的邻接矩阵+n^2 dijk

明天就出noip成绩莫名一种紧张感……

Code:

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<climits>
#include<cstring>
#include<vector>
using namespace std;
const int maxn=1510;
int n,m;
int x1,x2,y1,y2,f[maxn];
struct edge{int u,v,w;};
int mp[maxn][maxn];
short vis[maxn];
short can[maxn][maxn];
short Can[maxn];
int dx1[maxn],dx2[maxn],dy1[maxn],dy2[maxn];
void dijk(int s,int *d){
memset(vis,0,sizeof vis);
fill(d,d+1+n,INT_MAX>>1);d[s]=0;
for(int i=1;i<=n;i++){
int k=0,minn=d[0];
for(int j=1;j<=n;j++)if(!vis[j]&&minn>d[j])minn=d[j],k=j;
vis[k]=1;
for(int j=1;j<=n;j++)
d[j]=min(d[j],d[k]+mp[k][j]);

}
}
int dfs(int u){
if (vis[u])return f[u];
else{
vis[u]=1;
for(int v=1;v<=n;v++)if(can[u][v])
f[u]=max(f[u],mp[u][v]+dfs(v));
return f[u];
}
}
int main(){
scanf("%d%d",&n,&m);
memset(mp,0x3f,sizeof mp);
scanf("%d%d%d%d",&x1,&y1,&x2,&y2);
for(int i=1;i<=m;i++){
int u,v,w;scanf("%d%d%d",&u,&v,&w);
mp[u][v]=mp[v][u]=w;
}for(int i=1;i<=n;++i)mp[i][i]=0;
dijk(x1,dx1);
dijk(y1,dy1);
dijk(x2,dx2);
dijk(y2,dy2);
for(int u=1;u<=n;u++)
for(int v=1;v<=n;v++)
if(u!=v&&dx1[u]+mp[u][v]+dy1[v]==dx1[y1]&&
(dx2[u]+mp[u][v]+dy2[v]==dx2[y2]||dy2[u]+mp[u][v]+dx2[v]==dx2[y2]))
can[u][v]=1;
int ans=0;memset(vis,0,sizeof vis);
for(int i=1;i<=n;i++)ans=max(ans,dfs(i));
cout<<ans<<endl;
return 0;
}