[BZOJ] 1648: [Usaco2006 Dec]Cow Picnic 奶牛野餐

The cows are having a picnic! Each of Farmer John‘s K (1 <= K <= 100) cows is grazing in one of N (1 <= N <= 1,000) pastures, conveniently numbered 1...N. The pastures are connected by M (1 <= M <= 10,000) one-way paths (no path connects a pasture to itself). The cows want to gather in the same pasture for their picnic, but (because of the one-way paths) some cows may only be able to get to some pastures. Help the cows out by figuring out how many pastures are reachable by all cows, and hence are possible picnic locations.

* Line 1: Three space-separated integers, respectively: K, N, and M * Lines 2..K+1: Line i+1 contains a single integer (1..N) which is the number of the pasture in which cow i is grazing. * Lines K+2..M+K+1: Each line contains two space-separated integers, respectively A and B (both 1..N and A != B), representing a one-way path from pasture A to pasture B.

 第1行输入K，N，M.接下来K行，每行一个整数表示一只奶牛所在的牧场编号．接下来M行，每行两个整数，表示一条有向路的起点和终点

* Line 1: The single integer that is the number of pastures that are reachable by all cows via the one-way paths.

    所有奶牛都可到达的牧场个数

Silver

Analysis

DFS模拟奶牛走路就行了

Code

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<cstring>
 4 #define maxn 100000
 5 using namespace std;
 6 
 7 struct edge{
 8     int from,v;
 9 }e[maxn];
10 
11 int mark[maxn],cow[maxn],k,n,m;
12 bool book[maxn];
13 
14 int tot,first[maxn];
15 void insert(int u,int v){tot++;e[tot].from = first[u],e[tot].v = v,first[u] = tot;}
16 
17 void dfs(int now){
18     mark[now]++;
19     for(int i = first[now];i;i = e[i].from){
20         int v = e[i].v;
21         if(!book[v]){
22             book[v] = true;
23             dfs(v);
24         }
25     }
26 }
27 
28 int main(){
29     scanf("%d%d%d",&k,&n,&m);
30     
31     for(int i = 1;i <= k;i++)
32         scanf("%d",&cow[i]);
33     
34     for(int i = 1;i <= m;i++){
35         int a,b;
36         scanf("%d%d",&a,&b);
37         insert(a,b);
38     }
39     
40     for(int i = 1;i <= k;i++){
41         memset(book,false,sizeof(book));
42         book[cow[i]] = true;
43         dfs(cow[i]);
44     }
45     
46     int ans = 0;
47     for(int i = 1;i <= n;i++) if(mark[i] == k) ans++;
48     cout << ans;
49     
50     return 0;
51 }

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