最优贸易 

 1 #include<iostream>
 2 #include<cstdio>
 3 using namespace std;
 4 const int maxn=1e5+7;
 5 const int maxm=5e5+7;
 6 const int inf=0x7f7f7f7f;
 7 int n,m,num;
 8 int head[maxn],val[maxn],f[maxn],mi[maxn];
 9 int read(){
10     int f=1;int x=0;char s=getchar();
11     while(s<'0'||s>'9') {if(s=='-') f=-1;s=getchar();}
12     while(s>='0'&&s<='9'){x=x*10+s-'0';s=getchar();}
13     x*=f;
14     return x;
15 }
16 struct Edge{
17     int next,to;
18 }edge[maxm];
19 void add(int from,int to){
20     edge[++num].next=head[from];
21     edge[num].to=to;
22     head[from]=num;
23 }
24 void dfs(int x,int pre,int minn){
25     bool flag=1;
26     minn=min(minn,val[x]);
27     if(mi[x]>minn){mi[x]=minn;flag=false;}
28     int maxx=max(f[pre],val[x]-minn);
29     if(f[x]<maxx){f[x]=maxx;flag=false;}
30     if(flag==true) return;
31     for(int i=head[x];i;i=edge[i].next){
32         int v=edge[i].to;
33         dfs(v,x,minn);
34     }
35 }
36 int main(){
37     cin>>n>>m;
38     for(int i=1;i<=n;i++) cin>>val[i];
39     for(int i=1;i<=m;i++){
40         int x,y,z;x=read();y=read();z=read();
41         if(z==1) add(x,y);
42         if(z==2) {add(x,y);add(y,x);}
43     }
44     for(int i=1;i<=n;i++) mi[i]=inf;
45     dfs(1,0,inf);
46     cout<<f[n]<<endl;
47     return 0;
48 }

 

posted @ 2018-09-01 17:09  lcan  阅读(257)  评论(0)    收藏  举报