HDU 1815 Building roads

二分答案 + 2-SAT验证

POJ 稳过，HDU C++ 超时，G++ 550ms左右AC

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

const int maxn=1000+10;
int N,A,B;
int left,right,mid;
int s1x,s1y,s2x,s2y;
struct point
{
    int x,y;
    int p_s1;
    int p_s2;
}p[maxn];
int Hx[maxn],Hy[maxn];
int Lx[maxn],Ly[maxn];

stack<int>S;
vector<int>G[maxn];
vector<int>FG[maxn];
int Belong[maxn];
int flag[maxn];
int Block;

int dis1,dis2,dis3;

void init()
{
    for(int i=0;i<maxn;i++) G[i].clear();
    for(int i=0;i<maxn;i++) FG[i].clear();
    memset(Belong,0,sizeof Belong);
    memset(flag,0,sizeof flag);
    while(!S.empty()) S.pop();
    Block=0;
}

void addEgde(int x,int y)
{
    G[x].push_back(y);
    FG[y].push_back(x);
}

int Dis(int x1,int y1,int x2,int y2)
{
    return abs(x1-x2)+abs(y1-y2);
}

void read()
{
    scanf("%d%d%d%d",&s1x,&s1y,&s2x,&s2y);
    for(int i=0;i<N;i++)
        scanf("%d%d",&p[i].x,&p[i].y);
    for(int i=1;i<=A;i++)
    {
        scanf("%d%d",&Hx[i],&Hy[i]);
        Hx[i]--;Hy[i]--;
    }
    for(int i=1;i<=B;i++)
    {
        scanf("%d%d",&Lx[i],&Ly[i]);
        Lx[i]--;Ly[i]--;
    }
}

void dfs1(int now)
{
    flag[now]=1;
    for(int i=0;i<G[now].size();i++)
        if(!flag[G[now][i]])
            dfs1(G[now][i]);
    S.push(now);
}

void dfs2(int now)
{
    Belong[now]=Block;
    for(int i=0;i<FG[now].size();i++)
        if(!Belong[FG[now][i]])
            dfs2(FG[now][i]);
}

bool judge()
{
    for(int i=0;i<2*N;i++) if(!flag[i]) dfs1(i);
    while(!S.empty())
    {
        int Top=S.top(); S.pop();
        if(!Belong[Top])
        {
            Block++;
            dfs2(Top);
        }
    }
    for(int i=0;i<N;i++)
        if(Belong[2*i]==Belong[2*i+1])
            return 0;
    return 1;
}

void solve()
{
    left=0;right=8000000;
    int ans=-1;
    while(left<=right)
    {
        mid=(left+right)/2;
        init();


        for(int i=0;i<N;i++){
            for(int j=i+1;j<N;j++)
            {
                int pi_s1=p[i].p_s1;
                int pi_s2=p[i].p_s2;
                int pj_s1=p[j].p_s1;
                int pj_s2=p[j].p_s2;
                int s1_s2=Dis(s1x,s1y,s2x,s2y);

                if(pi_s1+pj_s1>mid) {
                    addEgde(2*i,2*j+1);
                    addEgde(2*j,2*i+1);
                }

                if(pi_s2+pj_s2>mid) {
                    addEgde(2*i+1,2*j);
                    addEgde(2*j+1,2*i);
                }

                if(pi_s1+s1_s2+pj_s2>mid) {
                    addEgde(2*i,2*j);
                    addEgde(2*j+1,2*i+1);
                }

                if(pi_s2+s1_s2+pj_s1>mid) {
                    addEgde(2*i+1,2*j+1);
                    addEgde(2*j,2*i);
                }
            }

        }


        for(int i=1;i<=A;i++)
        {
            addEgde(2*Hx[i],2*Hy[i]+1);
            addEgde(2*Hy[i]+1,2*Hx[i]);
            addEgde(2*Hx[i]+1,2*Hy[i]);
            addEgde(2*Hy[i],2*Hx[i]+1);
        }
        for(int i=1;i<=B;i++)
        {
            addEgde(2*Lx[i],2*Ly[i]);
            addEgde(2*Ly[i],2*Lx[i]);
            addEgde(2*Lx[i]+1,2*Ly[i]+1);
            addEgde(2*Ly[i]+1,2*Lx[i]+1);
        }
        if(judge()) ans=mid,right=mid-1;
        else left=mid+1;
    }
    printf("%d
",ans);
}
int main()
{
    while(~scanf("%d%d%d",&N,&A,&B)) 
    {
        read();
        for(int i=0;i<N;i++)
        {
            p[i].p_s1=Dis(p[i].x,p[i].y,s1x,s1y);
            p[i].p_s2=Dis(p[i].x,p[i].y,s2x,s2y);
        }
        solve();
    }
    return 0;
}