HDU 1007 Quoit Design

题解：最近点对模板

#include <cstdio>

#include <cmath>

#include <algorithm>

using namespace std;

typedef double D;

struct Q{D x,y;}q[100001],sl[10],sr[10];

int cntl,cntr,lm,rm; D ans;

int cmp(Q p1,Q p2){return(p1.x>p2.x);}

D Cal(D x1,D y1,D x2,D y2){return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));}

void Mindis(int l, int r){

    if(l==r)return; D dis;

    if (l+1==r){

        dis=Cal(q[l].x,q[l].y,q[r].x,q[r].y);

        if(ans>dis)ans=dis; return;

    }

    int mid=(l+r)>>1,i,j;

    Mindis(l,mid); Mindis(mid+1,r);

    lm=mid+1-5; if(lm<l)lm=l; 

    rm=mid+5; if(rm>r)rm=r; 

    cntl=cntr=0;

    for(i=mid;i>=lm;i--){

        if(q[mid+1].x-q[i].x>=ans)break;

        sl[++cntl]=q[i];

    }

    for(i=mid+1;i<=rm;i++){

        if (q[i].x-q[mid].x>=ans)break;

        sr[++cntr]=q[i];

    }

    for(i=1;i<=cntl;i++)

        for(j=1;j<=cntr;j++){

            dis=Cal(sl[i].x,sl[i].y,sr[j].x,sr[j].y);

            if(dis<ans)ans=dis;

        }

}

int main(){

    int n,i;

    while (scanf("%d",&n)==1&&n){

        for(i=1;i<=n;i++)scanf("%lf%lf",&q[i].x,&q[i].y);

        sort(q+1,q+n,cmp);

        ans=Cal(q[1].x,q[1].y,q[2].x,q[2].y);

        Mindis(1,n); printf("%.2lf\n",ans/2.0);

    }

    return 0;

}