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

2016年4月11日 0 作者 CrazyKK

1648: [Usaco2006 Dec]Cow Picnic 奶牛野餐

Time Limit: 5 Sec  Memory Limit: 64 MB
Submit: 562  Solved: 352


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.



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


Sample Input

2 4 4
1 2
1 4
2 3
3 4


^ ^
| |
| |

The pastures are laid out as shown above, with cows in pastures 2 and 3.

Sample Output



思路:爆搜,从每个奶牛开始做dfs,统计每个点到达的次数,到达为k次的就是合法的牧场。 我一开始的思路有点麻烦,也是从每个奶牛做dfs,然后把所有路径上经过的奶牛所在地存到一个数组里,每次访问一个新的点,就把所有奶牛数组里存进这个点的set里。。。但是实际上并不需要知道有哪些奶牛。。所以一个计数数组足矣。