图论：2-SAT模板

 1 #include<cstdio>
 2 #include<vector>
 3 #include<cstring>
 4 using namespace std;
 5 
 6 const int maxn = _____;
 7 
 8 struct TwoSAT
 9 {
10     int n;
11     vector<int> G[maxn*2];
12     bool mark[maxn*2];
13     int S[maxn*2], c;
14 
15     bool dfs(int x)
16     {
17         if (mark[x^1]) return false;
18         if (mark[x]) return true;
19         mark[x] = true;
20         S[c++] = x;
21         for (int i = 0; i < G[x].size(); i++)
22             if (!dfs(G[x][i])) return false;
23         return true;
24     }
25 
26     void init(int n) // 一定要注意初始化的点数，别弄错
27     {
28         this->n = n;
29         for (int i = 0; i < n*2; i++) G[i].clear();
30         memset(mark, 0, sizeof(mark));
31     }
32 
33     // x = xval or y = yval
34     void add_clause(int x, int xval, int y, int yval) // 编号从0~n-1
35     {
36         x = x * 2 + xval;
37         y = y * 2 + yval;
38         G[x^1].push_back(y);
39         G[y^1].push_back(x);
40     }
41 
42     bool solve()
43     {
44         for(int i = 0; i < n*2; i += 2)
45             if(!mark[i] && !mark[i+1])
46             {
47                 c = 0;
48                 if(!dfs(i))
49                 {
50                     while(c > 0) mark[S[--c]] = false;
51                     if(!dfs(i+1)) return false;
52                 }
53             }
54         return true;
55     }
56 };
57 
58 TwoSAT solver;
59 ////////////////////////////////////////////////////
60 //二分搜索，2-SAT中经常会用到
61         int L=____,R=____;
62         while(L < R)
63         {
64             int M = L + (R-L+1)/2;
65             if(test(M)) L = M; // M满足条件的话test返回真
66             else R = M-1;
67         }
68         printf("%d\n",L);