POJ 3268 Silver Cow Party（取反最短路）

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#include<iostream>
#include<cstdio>
#include<queue>
#include<vector>
#include<cstring>
using namespace std;
const int maxn = 1005;
#define inf 1e9
vector<pair<int,int> >e1[maxn];
vector<pair<int,int> >e2[maxn];
int d1[maxn],d2[maxn];
int vis[maxn];
int n,m,s;
void spfa(vector<pair<int,int> >*e,int d[])
{
memset(vis,0,sizeof(vis));
queue<int>q;
for(int i = 0;i<=n;i++)d[i]=inf;
d[s]=0;
q.push(s);
while(!q.empty())
{
int u = q.front();q.pop();
vis[u]=0;
for(int i = 0;i<e[u].size();i++)
{
int v = e[u][i].first;
int w = e[u][i].second;
if(d[v]>d[u]+w)
{
d[v]=d[u]+w;
if(!vis[v])
{
vis[v]=1;
q.push(v);
}
}
}
}
}
int main()
{
scanf("%d%d%d",&n,&m,&s);
for(int i = 0;i<m;i++)
{
int u,v,w;
scanf("%d%d%d",&u,&v,&w);
e1[u].push_back(make_pair(v,w));
e2[v].push_back(make_pair(u,w));
}
spfa(e1,d1);
spfa(e2,d2);
int ans = 0;
for(int i = 1;i<=n;i++)
ans = max(ans,d1[i]+d2[i]);
printf("%dn",ans);
}