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);