HDU 6697 Closest Pair of Segments (line segment)

First of all most likely to think violence is an enumeration of all segments N2 to find the minimum, but it will do a lot of wasted effort. We can first sorting line, such that the leftmost end in accordance with the x-axis y-axis segment ordering, then we can define all segments in the segment of the rectangular frame may have only a minimum value, for each query i-th segment the closest distance, if the difference x x left-most point of the j-th segment of the i-th right-most point of the segment is greater than ans, it can directly break, after the enumeration is no meaning, must be greater than ans, so the addition of this part of the pruning complexity to compress a large part.

  1 //        ——By DD_BOND
  2 
  3 //#include<bits/stdc++.h>
  4 //#include<unordered_map>
  5 //#include<unordered_set>
  6 #include<functional>
  7 #include<algorithm>
  8 #include<iostream>
  9 //#include<ext/rope>
 10 #include<iomanip>
 11 #include<climits>
 12 #include<cstring>
 13 #include<cstdlib>
 14 #include<cstddef>
 15 #include<cstdio>
 16 #include<memory>
 17 #include<vector>
 18 #include<cctype>
 19 #include<string>
 20 #include<cmath>
 21 #include<queue>
 22 #include<deque>
 23 #include<ctime>
 24 #include<stack>
 25 #include<map>
 26 #include<set>
 27 
 28 #define fi first
 29 #define se second
 30 #define MP make_pair
 31 #define pb push_back
 32 
 33 #pragma GCC optimize(3)
 34 #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
 35 
 36 using namespace std;
 37 
 38 typedef long long ll;
 39 
 40 const int MAXN=1e5+10;
 41 const double eps=1e-8;
 42 const double pi=acos(-1.0);
 43 const ll INF=0x3f3f3f3f3f3f3f3f;
 44 
 45 inline int dcmp(double x){
 46     if(fabs(x)<eps)    return 0;
 47     return (x>0? 1: -1);
 48 }
 49 
 50 inline double sqr(double x){ return x*x; }
 51 
 52 struct Point{
 53     double x,y; int id;
 54     Point(){ x=0,y=0; }
 55     Point(double _x,double _y):x(_x),y(_y){}
 56     void input(){ scanf("%lf%lf",&x,&y); }
 57     void output(){ printf("%.2f %.2f\n",x,y); }
 58     inline bool operator <(const Point &b)const{
 59         return (dcmp(x-b.x)==0? dcmp(y-b.y)<0 : x<b.x);
 60     }
 61     inline Point operator -(const Point &b)const{
 62         returnPoint (xb.x, Y- by);
 63 is      }
 64      inline Double LEN2 () {     // square of the length 
65          return SQR (X) + SQR (Y);
 66      }
 67      inline Double len () {    // length 
68          return sqrt (LEN2 ());
 69      }
 70  };
 71 is  
72 inline Double Cross (Point A, Point B) {     // cross product 
73 is      return AX-AY * * by BX;
 74  }
 75  
76 inlineDouble DOT (Point A, Point B) {     // dot product 
77      return AX + AY * * b.x by;
 78  }
 79  
80 inline Double DIS (Point A, Point B) {     // distance between two points 
81      Point P BA =;     return p.len ();
 82  }
 83  
84  struct Line {
 85      Point S, E;
 86      Line () {}
 87      Line (Point _s, _E Point): S (_s), E (_E) {} // two points define a line 
88      void INPUT () {
 89          s.input ();
 90         e.input ();
 91 is      }
 92      Double length () {
 93          return DIS (S, E);
 94      }
 95  };
 96  
97 inline Double point_to_line (Point P, Line A) {     // point to the straight line distance 
98      return FABS (Cross (Pa.s, AE-AS) / a.length ());
 99  }
 100  
101 inline Double point_to_seg (point P, line A) {     // points to the line segment 
102      IF (dCMP (dOT (Pa.s , AE-AS)) < 0 || dCMP (DOT (pa.e, AS-AE)) < 0 )
 103         return min(dis(p,a.e),dis(p,a.s));
104     return point_to_line(p,a);
105 }
106 
107 inline double seg_to_seg(Line u,Line v){
108     return min( min(point_to_seg(u.s,v),point_to_seg(u.e,v)), min( point_to_seg(v.s,u),point_to_seg(v.e,u)) );
109 }
110 
111 Line line[MAXN];
112 
113 bool cmp(Line a,Line b){
114     return a.s<b.s;
115 }
116 
117 int main(void){
118     int T;  scanf("%d",&T);
119     while(T--){
120         int n;  scanf("%d",&n);
121         for(int i=0;i<n;i++){
122             line[i].input();
123             if(line[i].e<line[i].s) swap(line[i].s,line[i].e);
124         }
125         sort(line,line+n,cmp);
126         double ans=1e10;        
127         for(int i=0;i<n;i++)
128             for(int j=i+1;j<n;j++){
129                 if(dcmp(line[j].s.x-line[i].e.x-ans)>0)    break;
130                 ans=min(ans,seg_to_seg(line[i],line[j]));
131             }
132         printf("%.12f\n",ans);
133     }
134     return 0;
135 }