POJ 2723 HDU 1816 Get Luffy Out

二分答案 + 2-SAT验证

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

const int maxn=60000+10;

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

int doorX[maxn],doorY[maxn];
int keyX[maxn],keyY[maxn];
int left,right,mid,ans;

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

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*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<2*N; i++)
        if(Belong[2*i]==Belong[2*i+1])
            return 0;
    return 1;
}

void read()
{
    for(int i=0;i<N;i++)
        scanf("%d%d",&keyX[i],&keyY[i]);

    for(int i=0;i<M;i++)
        scanf("%d%d",&doorX[i],&doorY[i]);
}

int main()
{
    while(~scanf("%d%d",&N,&M))
    {
        if(!N&&!M) break;
        read();
        left=0,right=M;
        while(left<=right)
        {
            mid=(left+right)/2;
            init();
            for(int i=0;i<N;i++)
            {
                addEdge(2*keyX[i]+1,2*keyY[i]);
                addEdge(2*keyY[i]+1,2*keyX[i]);
            }
            for(int i=0;i<mid;i++)
            {
                addEdge(2*doorX[i],2*doorY[i]+1);
                addEdge(2*doorY[i],2*doorX[i]+1);
            }

            if(judge()){ans=mid;left=mid+1;}
            else right=mid-1;
        }
        printf("%d
",ans);
    }
    return 0;
}