1061: [Noi2008]志愿者招募

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<queue>
 5 using namespace std;
 6 
 7 const int INF=0x7f7f7f7f;
 8 const int T=1004;
 9 const int N=1005;
10 const int M=50005;
11 
12 struct Edge
13 {
14     int from,to,v,c,next;//from点到to点 v代表容量 c代表花费 next下一条边
15 }E[M];
16 int node=1;
17 int head[N],from[N],dis[N],vis[N];
18 
19 int n,m,ans;
20 
21 void ins(int from,int to,int v,int c)
22 {
23     node++;
24     E[node]=(Edge){from,to,v,c,head[from]};
25     head[from]=node;
26 }
27 
28 void insert(int from,int to,int v,int c)
29 {
30     ins(from,to,v,c);ins(to,from,0,-c);
31 }
32 
33 bool spfa()
34 {
35     queue<int> Q;
36     memset(dis,0x7f,sizeof(dis));
37     Q.push(0);dis[0]=0;vis[0]=1;
38     while(!Q.empty())
39     {
40         int q=Q.front();Q.pop();
41         for(int i=head[q];i;i=E[i].next)
42             if(E[i].v>0&&dis[q]+E[i].c<dis[E[i].to])
43             {
44                 dis[E[i].to]=dis[q]+E[i].c;
45                 from[E[i].to]=i;
46                 if(!vis[E[i].to])
47                 {
48                     Q.push(E[i].to);
49                     vis[E[i].to]=1;
50                 }
51             }
52         vis[q]=0;
53     }
54     return dis[T]!=INF;
55 }
56 
57 void mcf()
58 {
59     int x=INF;
60     for(int i=from[T];i;i=from[E[i].from])
61         x=min(E[i].v,x);
62     for(int i=from[T];i;i=from[E[i].from])
63     {
64         ans+=x*E[i].c;
65         E[i].v-=x;E[i^1].v+=x;
66     }
67 }
68 
69 int main()
70 {
71     scanf("%d %d",&n,&m);
72     int l=0,r;
73     for(int i=1;i<=n;i++)
74     {
75         scanf("%d",&r);
76         int x=r-l;
77         if(x>0) insert(0,i,x,0);
78         else insert(i,T,-x,0);
79         insert(i+1,i,INF,0);
80         l=r;
81     }
82     insert(n+1,T,l,0);
83     for(int i=1;i<=m;i++)
84     {
85         int s,t,c;
86         scanf("%d %d %d",&s,&t,&c);
87         insert(s,t+1,INF,c);
88     }
89     while(spfa()) mcf();
90     printf("%d\n",ans);
91     return 0;
92 }