NOIP2009 最优贸易

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 const int maxn = 100010;
 4 struct arc{
 5     int to,next;
 6     bool ok;
 7     arc(int x = 0,int y = -1,bool o = false){
 8         to = x;
 9         next = y;
10         ok = o;
11     }
12 }e[1000010];
13 int head[maxn],theMin[maxn],theMax[maxn],value[maxn],tot,n,m;
14 void add(int u,int v,bool a,bool b){
15     e[tot] = arc(v,head[u],a);
16     head[u] = tot++;
17     e[tot] = arc(u,head[v],b);
18     head[v] = tot++;
19 }
20 queue<int>q;
21 bool in[maxn];
22 void spfa(){
23     while(!q.empty()) q.pop();
24     memset(theMin,127,sizeof(theMin));
25     memset(in,false,sizeof(in));
26     theMin[1] = value[1];
27     q.push(1);
28     while(!q.empty()){
29         int u = q.front();
30         q.pop();
31         in[u] = false;
32         for(int i = head[u]; ~i; i = e[i].next){
33             if(e[i].ok && theMin[e[i].to] > min(theMin[u],value[e[i].to])){
34                 theMin[e[i].to] = min(theMin[u],value[e[i].to]);
35                 if(!in[e[i].to]){
36                     in[e[i].to] = true;
37                     q.push(e[i].to);
38                 }
39             }
40         }
41     }
42 }
43 void spfa2(){
44     while(!q.empty()) q.pop();
45     memset(in,false,sizeof(in));
46     memset(theMax,0,sizeof(theMax));
47     theMax[n] = value[n];
48     q.push(n);
49     while(!q.empty()){
50         int u = q.front();
51         q.pop();
52         in[u] = false;
53         for(int i = head[u]; ~i; i = e[i].next){
54             if(e[i^1].ok && theMax[e[i].to] < max(theMax[u],value[e[i].to])){
55                 theMax[e[i].to] = max(theMax[u],value[e[i].to]);
56                 if(!in[e[i].to]){
57                     in[e[i].to] = true;
58                     q.push(e[i].to);
59                 }
60             }
61         }
62     }
63 }
64 int main(){
65     int u,v,o;
66     while(~scanf("%d %d",&n,&m)){
67         for(int i = 1; i <= n; ++i)
68             scanf("%d",value+i);
69         memset(head,-1,sizeof(head));
70         for(int i = tot = 0; i < m; ++i){
71             scanf("%d %d %d",&u,&v,&o);
72             add(u,v,o >= 1,o >= 2);
73         }
74         spfa();
75         spfa2();
76         int ans = 0;
77         for(int i = 1; i <= n; ++i)
78             ans = max(ans,theMax[i] - theMin[i]);
79         printf("%d\n",ans);
80     }
81     return 0;
82 }