[Bzoj1143][CTSC2008]祭祀river

题目链接

思路清晰的发现题意是求最小路径覆盖。

最少路径覆盖:是指在一个有向图中,找出最少的几条路径,用它们来覆盖全图。

先闭包处理一下,然后二分图跑一下。

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 typedef long long ll;
 4 const unsigned int maxn = 100 + 10;
 5 const double PI = acos(-1);
 6 int g[maxn][maxn], L[maxn], vis[maxn];
 7 int n;
 8 int dfs(int x) {
 9     for (int i = 1; i <= n; i++) {
10         if (g[x][i] && vis[i] == 0) {
11             vis[i] = 1;
12             if (L[i] == -1 || dfs(L[i])) {
13                 L[i] = x;
14                 return 1;
15             }
16         }
17     }
18     return 0;
19 }
20 int xyl() {
21     int ans = 0;
22     memset(L, -1, sizeof(L));
23     for (int i = 1; i <= n; i++) {
24         memset(vis, 0, sizeof(vis));
25         if (dfs(i))
26             ans++;
27     }
28     return ans;
29 }
30 int main() {
31     int  m, x, y;
32     scanf("%d%d", &n, &m);
33     for (int i = 1; i <= m; i++)
34         scanf("%d%d", &x, &y), g[x][y] = 1;
35     for (int k = 1; k <= n; k++)
36         for (int i = 1; i <= n; i++)
37             for (int j = 1; j <= n; j++)
38                 g[i][j] |= g[i][k] & g[k][j];
39     printf("%d\n", n - xyl());
40 }

 

posted @ 2019-08-30 21:01  祈梦生  阅读(59)  评论(0编辑  收藏