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);
