首先算出mp[i][j]:
以i为最高点,i到j的最短距离是多少。
然后对于每次询问,枚举最高点。
结果就为min(mp[i][st]+mp[i][ed]+val[i]);
但是这个题我用SFL优化了一下。。
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<iostream>
#include<algorithm>
#include<vector>
#include<queue>
#include<map>
#include<math.h>
#include<deque>
using namespace std;
#define maxn 1010
#define maxm 20020
#define LL long long
#define INF (LL)99999999999999
struct listt
{
int u,v;
LL w;
int next;
}edge[maxm*2];
int head[maxn];
int nums;
void init()
{
memset(head,-1,sizeof(head));
nums=1;
}
void add(int u,int v,LL w)
{
// cout<<"add"<<u<<" "<<v<<" "<<w<<endl;
edge[nums].u=u;
edge[nums].v=v;
edge[nums].w=w;
edge[nums].next=head[u];
head[u]=nums++;
}
LL mp[maxn][maxn];
LL val[maxn];
deque<int>que;
LL dist[maxn];
int vis[maxn];
int n;
void spfa(int st)
{
for(int i=1;i<=n;i++)dist[i]=INF;
memset(vis,0,sizeof(vis));
dist[st]=0;
que.push_back(st);
vis[st]=1;
while(!que.empty())
{
int x=que.front();
que.pop_front();
vis[x]=0;
// cout<<x<<"-"<<endl;;
for(int i=head[x];i!=-1;i=edge[i].next)
{
int y=edge[i].v;
// cout<<i<<" "<<y<<" "<<val[y]<<" "<<val[x]<<endl;
if(val[y]>val[st])continue;
if(dist[y]>dist[x]+edge[i].w)
{
dist[y]=dist[x]+edge[i].w;
if(!vis[y])
{
if(!que.empty())
{
if(dist[y]>dist[que.front()])que.push_back(y);
else que.push_front(y);
}
else que.push_back(y);
vis[y]=1;
}
}
}
}
// printf("_________________%d\n",st);
for(int i=1;i<=n;i++)
{
mp[st][i]=dist[i];
// printf("%lld ",mp[st][i]);
}
// cout<<endl;
}
struct lisq
{
int st;
int ed;
LL minn;
}Q[maxm];
int main()
{
int m,q;
while(~scanf("%d%d",&n,&m)&&(n||m))
{
init();
while(!que.empty())que.pop_back();
for(int i=1;i<=n;i++)
{
for(int j=1;j<=n;j++)
{
mp[i][j]=INF;
}
mp[i][i]=0;
}
for(int i=1;i<=n;i++)
scanf("%lld",&val[i]);
int u,v;
LL w;
for(int i=1;i<=m;i++)
{
scanf("%d%d%lld",&u,&v,&w);
add(u,v,w);
add(v,u,w);
}
scanf("%d",&q);
int st,ed;
for(int i=1;i<=q;i++)
{
scanf("%d%d",&Q[i].st,&Q[i].ed);
Q[i].minn=INF;
}
for(int i=1;i<=n;i++)
{
spfa(i);
for(int j=1;j<=q;j++)
{
Q[j].minn=min(Q[j].minn,mp[i][Q[j].st]+mp[i][Q[j].ed]+val[i]);
}
}
for(int i=1;i<=q;i++)
{
if(Q[i].minn<INF)printf("%lld\n",Q[i].minn);
else puts("-1");
}
cout<<endl;
}
return 0;
}