poj3714——Raid

题意：给定两组坐标，求两组之间的最小距离。

思路：即最近点对。

参考算法导论，

http://blog.csdn.net/jw72jw/archive/2011/01/22/6158679.aspx

http://blog.csdn.net/smsmn/archive/2010/10/25/5963487.aspx

#include<iostream> #include<cstdio> #include<cstring> #include<algorithm> #include<cmath> using namespace std; #define maxn 200005 #define maxcost 1e100 class point { public: double x,y; int flag; }; point p[maxn]; bool cmp1(point a,point b) { if(a.x<b.x ||a.x==b.x&&a.y<b.y)return true; return false; } double dist(point a,point b) { return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)); } double min_dis(int l,int r) { int i,j; double resultl =0,resultr=0,minlen=maxcost; if(r>l+2) { int mid=(l+r)>>1; double tempdis=maxcost; resultl=min_dis(l,mid); resultr=min_dis(mid,r); minlen=resultl<resultr?resultl:resultr; for(i=mid;i>=l&&p[i].x >p[mid].x-minlen;i--) { for(j=mid;j<=r&&p[j].x<p[mid].x+minlen;j++) { if(p[i].flag !=p[j].flag ) tempdis=dist(p[i],p[j]); if(tempdis<minlen) minlen=tempdis; } } } else { double dis; for(i=l;i<r;i++) for(j=1+i;j<=r;j++) { if(j==i) continue; if(p[i].flag !=p[j].flag ) { dis=dist(p[i],p[j]); minlen=minlen<dis?minlen:dis; } } } return minlen; } int main() { int n,ca; cin>>ca; while(ca--) { cin>>n; for(int i=1;i<=n;i++) { scanf("%lf%lf",&p[i].x,&p[i].y); p[i].flag =1;} for(int i=1+n;i<=n*2;i++) { scanf("%lf%lf",&p[i].x,&p[i].y); p[i].flag =2;} n*=2; sort(p+1,p+n+1,cmp1); double result=min_dis(1,n); printf("%.3f\n",result); } return 0; }