HDU1007：Quoit Design——题解

#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
typedef double dl;
const dl INF=1e20;
const int N=100001;
struct node{
    dl x;
    dl y;
}p[N],a[N],b[N],c[N];
bool cmp(node A,node B){
    return A.x<B.x;
}
inline dl dis(int i,int j){
    return sqrt(pow(b[i].x-c[j].x,2)+pow(b[i].y-c[j].y,2));
}
dl solve(int l,int r){
    if(l>=r)return INF;
    int mid=(l+r)>>1;
    dl x0=(p[mid].x+p[mid+1].x)/2.0;
    dl d=min(solve(l,mid),solve(mid+1,r));
    int l1=l,r1=mid+1,bnum=0,cnum=0;
    for(int i=l;i<=r;i++){
    if(l1<=mid&&(r1>r||p[l1].y<p[r1].y)){
        a[i]=p[l1++];
        if(x0-d<a[i].x)b[++bnum]=a[i];
    }else{
        a[i]=p[r1++];
        if(a[i].x<x0+d)c[++cnum]=a[i];
    }
    }
    for(int i=l;i<=r;i++)p[i]=a[i];

    for(int i=1,j=1;i<=bnum||j<=cnum;){
    if(i<=bnum&&(j>cnum||b[i].y<c[j].y)){
        for(int k=j-1;k>=1;k--){
        if(b[i].y-d>=c[k].y)break;
        d=min(d,dis(i,k));
        }
        i++;
    }else{
        for(int k=i-1;k>=1;k--){
        if(c[j].y-d>=b[k].y)break;
        d=min(d,dis(k,j));
        }
        j++;
    }
    }
    return d;
}
int main(){
    int n;
    while(scanf("%d",&n)!=EOF&&n){
    for(int i=1;i<=n;i++){
        scanf("%lf%lf",&p[i].x,&p[i].y);
    }
    sort(p+1,p+n+1,cmp);
    printf("%.2f\n",solve(1,n)/2.0);
    }
    return 0;
}