HDU 3622 Bomb Game(2-SAT)

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#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>#include<vector>#include<cmath>using namespace std;const double eps=1e-5;const int maxn=100+5;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){        this->n=n;        for(int i=0;i<2*n;i++) G[i].clear();        memset(mark,0,sizeof(mark));    }        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<2*n;i+=2){            if(!mark[i]&&!mark[i+1]){                c=0;                if(!dfs(i)){                    while(c) mark[s[--c]]=false;                    if(!dfs(i+1)) return false;                }            }        }        return true;    }};TwoSAT solver;struct point{int x,y;}points[maxn][2];int n;bool test(double diff){    solver.init(n);    for(int i=0;i<n;i++){        for(int a=0;a<2;a++){            for(int j=i+1;j<n;j++){                for(int b=0;b<2;b++){                    int x1=points[i][a].x,y1=points[i][a].y;                    int x2=points[j][b].x,y2=points[j][b].y;                    double r=sqrt(abs(x1-x2)*abs(x1-x2)+abs(y1-y2)*abs(y1-y2))/2;                    if(r+eps<diff) solver.add_clause(i,a^1,j,b^1);                }            }        }    }    return solver.solve();}int main(){    while(scanf("%d",&n)!=EOF)    {        for(int i=0;i<n;i++){            for(int j=0;j<2;j++)                scanf("%d%d",&points[i][j].x,&points[i][j].y);        }        double l=0.0,r=30000.0;        while(l+eps<r){            double mid=(l+r)/2;            if(test(mid)) l=mid;else r=mid;        }        printf("%.2f\n",l);    }    return 0;}
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