loj 1406(状态压缩)

题目链接:http://lightoj.com/volume_showproblem.php?problem=1406

思路:首先可以预处理出在每个顶点的状态的合法状态vis[u][state], 然后标记那些合法状态mark[state]。最后就是记忆化搜索了,对于当前状态state,我们有res = min(res, 1 + Solve(state ^ substate)), 其中substate为state的子状态,并且substate = (substate  - 1) & state.那么最终就是要求Solve((1 << n) - 1)了。

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <algorithm>
 5 #include <vector>
 6 using namespace std;
 7 
 8 int n, m;
 9 bool vis[16][1 << 16];
10 bool mark[1 << 16];
11 int dp[1 << 16];
12 vector<int > g[16];
13 
14 void dfs(int u, int state)
15 {
16     vis[u][state] = true;
17     mark[state] = true;
18     for (int i = 0; i < (int)g[u].size(); i++) {
19         int v = g[u][i];
20         if (!vis[v][state | (1 << v)]) {
21             dfs(v, state | (1 << v));
22         }
23     }
24 }
25 
26 int Solve(int state)
27 {
28     if (state == 0) return 0;
29     if (dp[state] != -1) return dp[state];
30     int res = 16;
31     for (int i = state; i > 0; i = (i - 1) & state) {
32         if (mark[i]) {
33             res = min(res, 1 + Solve(state ^ i));
34         }
35     }
36     return dp[state] = res;
37 }
38 
39 
40 int main()
41 {
42     int _case, t = 1;
43     scanf("%d", &_case);
44     while (_case--) {
45         scanf("%d %d", &n, &m);
46         for (int i = 0; i < n; i++) g[i].clear();
47         while (m--) {
48             int u, v;
49             scanf("%d %d", &u, &v);
50             u--, v--;
51             g[u].push_back(v);
52         }
53         memset(vis, false, sizeof(vis));
54         memset(mark, false, sizeof(mark));
55         for (int i = 0; i < n; i++) dfs(i, 1 << i);
56         memset(dp, -1, sizeof(dp));
57         printf("Case %d: %d\n", t++, Solve((1 << n) -1));
58     }
59     return 0;
60 }
View Code

 

 

posted @ 2014-01-22 16:45  ihge2k  阅读(241)  评论(0编辑  收藏  举报