BZOJ1916: [Usaco2010 Open]冲浪

 1 #include<stdio.h>
 2 #include<string.h>
 3 #include<stdlib.h>
 4 #include<algorithm>
 5 //#include<iostream>
 6 using namespace std;
 7 
 8 int n,m,K;
 9 #define maxm 300011
10 #define maxn 50011
11 struct Edge{int to,v,next;}edge[maxm];int first[maxn],back[maxn],le=2;
12 void in(int x,int y,int v,int* first) {Edge &e=edge[le];e.to=y;e.v=v;e.next=first[x];first[x]=le++;}
13 #define LL long long
14 int du[maxn],last[maxn];LL f[maxn][13],dis[maxn];
15 int x,y,v,que[maxn],head,tail;
16 const LL inf=1e15;
17 void play(int x)
18 {
19     for (int i=back[x];i;i=edge[i].next)
20     {
21         const Edge &e=edge[i];
22         du[e.to]--;
23         if (!du[e.to]) que[tail++]=e.to;
24     }
25     if (x==n)
26     {
27         for (int i=1;i<=K;i++) f[x][i]=-inf;
28         f[x][0]=0;return;
29     }
30     LL Max=-inf,Min=inf;
31     for (int j=0;j<=K;j++)
32     {
33         for (int i=first[x];i;i=edge[i].next)
34         {
35             const Edge &e=edge[i];
36             if (f[e.to][j]>=0) Max=max(Max,f[e.to][j]+e.v);
37             if (j && f[e.to][j-1]>=0) Min=min(Min,f[e.to][j-1]+e.v);
38         }
39         f[x][j]=Max<0?(Min<0?-inf:Min):(Min<0?Max:min(Max,Min));
40     }
41 }
42 int main()
43 {
44     scanf("%d%d%d",&n,&m,&K);
45     memset(du,0,sizeof(du));
46     for (int i=1;i<=m;i++)
47     {
48         scanf("%d%d%d",&x,&y,&v);
49         in(x,y,v,first);
50         in(y,x,v,back);
51         du[x]++;
52     }
53     head=tail=0;
54     for (int i=1;i<=n;i++) if (!du[i]) que[tail++]=i;
55     while (head!=tail) play(que[head++]);
56     printf("%lld\n",f[1][K]);
57     return 0;
58 }