图论：2-SAT模板

#include<cstdio>
#include<vector>
#include<cstring>
using namespace std;

const int maxn = _____;

struct TwoSAT
{
    int n;
    vector<int> G[maxn*2];
    bool mark[maxn*2];
    int S[maxn*2], c;

    bool dfs(int x)
    {
        if (mark[x^1]) return false;
        if (mark[x]) return true;
        mark[x] = true;
        S[c++] = x;
        for (int i = 0; i < G[x].size(); i++)
            if (!dfs(G[x][i])) return false;
        return true;
    }

    void init(int n) // 一定要注意初始化的点数，别弄错
    {
        this->n = n;
        for (int i = 0; i < n*2; i++) G[i].clear();
        memset(mark, 0, sizeof(mark));
    }

    // x = xval or y = yval
    void add_clause(int x, int xval, int y, int yval) // 编号从0~n-1
    {
        x = x * 2 + xval;
        y = y * 2 + yval;
        G[x^1].push_back(y);
        G[y^1].push_back(x);
    }

    bool solve()
    {
        for(int i = 0; i < n*2; i += 2)
            if(!mark[i] && !mark[i+1])
            {
                c = 0;
                if(!dfs(i))
                {
                    while(c > 0) mark[S[--c]] = false;
                    if(!dfs(i+1)) return false;
                }
            }
        return true;
    }
};

TwoSAT solver;
////////////////////////////////////////////////////
//二分搜索，2-SAT中经常会用到
        int L=____,R=____;
        while(L < R)
        {
            int M = L + (R-L+1)/2;
            if(test(M)) L = M; // M满足条件的话test返回真
            else R = M-1;
        }
        printf("%d
",L);