poj3160
http://poj.org/problem?id=3160
题意读懂是关键，he chould choose to enter and give out a gift and hear the words from the recipient, or bypass the room in silence.通过这句话知道当收礼者给予的反应是负值时可以不加，flymouse decided to choose only one of those rooms as the place to start his journey and follow directed paths to visit one room after another and give out gifts en passant until he could reach no more unvisited rooms.即起点只有一个，且一条路到底，即要我们寻找一条路径的尾节点出度为0，且路径中所有数值为正的节点的和最大。
明显是dfs，用max数组记录每一个节点到出度为0的节点的最大值，但是由于此图是有向图，可能会产生环，因此先用强连通缩点，在dfs找到最到值。
1 #include <stdio.h>
2 #include <memory.h>
3 #define SIZE 30001
4 #define MAX(a,b) ((a)>(b)?(a):(b))
5 struct node
6 {
7 int end;
8 node *next;
9 }edge[5*SIZE],*head[SIZE],*p,Edge[5*SIZE],*Head[SIZE],*q;
10 int feel[SIZE],root_stack[SIZE],stack[SIZE],init[SIZE],belong[SIZE],sum[SIZE],max[SIZE];
11 bool visit[SIZE];
12 int cnt,father,MAXER;
13 void bulid(int a,int b)
14 {
15 p->end=b;
16 p->next=head[a];
17 head[a]=p++;
18 }
19 void add(int a,int b)
20 {
21 q->end=b;
22 q->next=Head[a];
23 Head[a]=q++;
24 }
25 void Gabow(int key)
26 {
27 root_stack[++root_stack[0]]=stack[++stack[0]]=key;
28 init[key]=++cnt;
29 for(node*tmp=head[key];tmp;tmp=tmp->next)
30 {
31 if(!init[tmp->end])
32 Gabow(tmp->end);
33 else if(!belong[tmp->end])
34 while(init[root_stack[root_stack[0]]]>init[tmp->end])
35 --root_stack[0];
36 }
37 if(root_stack[root_stack[0]]==key)
38 {
39 ++father,--root_stack[0];
40 do
41 {
42 belong[stack[stack[0]]]=father;
43 if(feel[stack[stack[0]]]>0)
44 sum[father]+=feel[stack[stack[0]]];
45 }
46 while(stack[stack[0]--]!=key);
47 }
48 }
49 void dfs(int key)
50 {
51 visit[key]=true;
52 for(node *tmp=Head[key];tmp;tmp=tmp->next)
53 {
54 if(!visit[tmp->end])
55 dfs(tmp->end);
56 max[key]=MAX(max[key],max[tmp->end]);
57 }
58 max[key]+=sum[key];
59 MAXER=MAX(MAXER,max[key]);
60 }
61 void ini()
62 {
63 memset(head,NULL,sizeof(head));
64 memset(Head,NULL,sizeof(Head));
65 memset(visit,false,sizeof(visit));
66 memset(feel,0,sizeof(feel));
67 memset(root_stack,0,sizeof(root_stack));
68 memset(stack,0,sizeof(stack));
69 memset(init,0,sizeof(init));
70 memset(belong,0,sizeof(belong));
71 memset(sum,0,sizeof(sum));
72 memset(max,0,sizeof(max));
73 }
74 int main()
75 {
76 int n,m;
77 while(scanf("%d %d",&n,&m)==2)
78 {
79 for(int i=0;i<n;++i)
80 scanf("%d",&feel[i]);
81 p=edge;
82 for(int i=0,a,b;i<m;++i)
83 {
84 scanf("%d %d",&a,&b);
85 bulid(a,b);
86 }
87 cnt=father=0;
88 for(int i=0;i<n;++i)
89 if(!init[i])
90 Gabow(i);
91 q=Edge;
92 for(int i=0;i<n;++i)
93 for(node*tmp=head[i];tmp;tmp=tmp->next)
94 if(belong[i]!=belong[tmp->end])
95 add(belong[i],belong[tmp->end]);
96 MAXER=-(1<<31);
97 for(int i=1;i<=father;++i)
98 if(!visit[i])
99 dfs(i);
100 printf("%d\n",MAXER);
101 ini();
102 }
103 return 0;
104 }
