2-SAT入门 poj2749 Building roads

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

typedef pair<int,int> Point;
//点的标号从0开始到2n-1
const int maxn = 500 + 10 ;
const int maxm = 1000 + 10 ;
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 0;
        if(mark[x  ]) return 1;
        mark[x] = 1;
        S[c++]  = x;
        for (int i = 0; i < G[x].size(); ++i)
            if(!dfs(G[x][i])) return 0;
        return 1;
    }

    void init(int n){
        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){
        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]] = 0;
                    if(!dfs(i+1))
                        return 0;
                }
            }
        return 1;
    }
};

TwoSAT TSAT;
Point S[3],P[maxn];
pair<int,int> hate[maxm],like[maxm];

int N,A,B,SS;

int dis(Point P,Point Q){return abs(P.first-Q.first)+abs(P.second-Q.second);}

bool ok(int lim){
    TSAT.init(N);
    for (int i = 0; i < A; ++i){
        TSAT.add_clause(hate[i].first,0,hate[i].second,0);
        TSAT.add_clause(hate[i].first,1,hate[i].second,1);
    }
    for (int i = 0; i < B; ++i){
        TSAT.add_clause(like[i].first,0,like[i].second,1);
        TSAT.add_clause(like[i].first,1,like[i].second,0);
    }
    for (int i = 0; i < N; ++i)
        for (int j = i+1; j < N; ++j){
            int i0 = dis(P[i],S[0]),
                i1 = dis(P[i],S[1]),
                j0 = dis(P[j],S[0]),
                j1 = dis(P[j],S[1]);
            if(i0+j0>lim)
                TSAT.add_clause(i,1,j,1);
            if(i1+j1>lim)
                TSAT.add_clause(i,0,j,0);
            if(i0+SS+j1>lim)
                TSAT.add_clause(i,1,j,0);
            if(i1+SS+j0>lim)
                TSAT.add_clause(i,0,j,1);
        }
    return TSAT.solve();
}

int main()
{

    Point S1,S2;
    while(cin>>N>>A>>B){
        cin>>S[0].first>>S[0].second>>S[1].first>>S[1].second;
        SS=dis(S[0],S[1]);
        for (int i = 0; i < N; ++i)
            cin>>P[i].first>>P[i].second;

        for (int i = 0; i < A; ++i){
            cin>>hate[i].first>>hate[i].second;
            hate[i].first--;
            hate[i].second--;
        }
        for (int i = 0; i < B; ++i){
            cin>>like[i].first>>like[i].second;
            like[i].first--;
            like[i].second--;
        }

        if(!ok(4000000)){
            cout<<-1<<endl;
            continue;
        }

        int l=0,r=4000000,mid=(l+r)>>1;
        for(;l<r-1;mid=(l+r)>>1)
            if(ok(mid))
                r=mid;
            else
                l=mid;

        cout<<r<<endl;
    }
    return 0;
}