hdu 1007(最近点对)

 1 /*
 2 *  题目要求：求最近点对  
 3 */
 4 
 5 #include <cmath>
 6 #include <cstdio>
 7 #include <cstdlib>
 8 #include <iostream>
 9 #include <algorithm>
10 
11 using namespace std;
12 
13 const int N = 100005;
14 const double INF = 1e15;
15 
16 struct point {
17     double x;
18     double y;
19 }p[N];
20 int tmp[N];
21 
22 double dis(point A, point B) {
23     return sqrt((A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y));
24 }
25 
26 int cmp(const point &a, const point &b) {
27     if (a.x != b.x) return a.x < b.x;
28     return a.y < b.y;
29 }
30 
31 int cmp1(const int &a, const int &b) {
32     return p[a].y < p[b].y;
33 }
34 
35 double min(double a, double b) {
36     return a > b ? b : a;
37 }
38 
39 double closestPair(int left, int right) {
40     double d = INF;
41     if (left == right) return d;
42     if (left+1 == right) return dis(p[left], p[right]);
43     int mid = (left + right) >> 1;
44     double d1 = closestPair(left, mid);
45     double d2 = closestPair(mid+1, right);
46     d = min(d1, d2);
47     int k = 0;
48     for (int i=left; i<=right; ++i) {
49         if (fabs(p[mid].x- p[i].x) <= d) tmp[k++] = i;
50     }
51     sort(tmp, tmp+k, cmp1);
52     for (int i=0; i<k; ++i) {
53         for (int j=i+1; j<k && p[tmp[j]].y-p[tmp[i]].y<d; ++j) {
54             double d3 = dis(p[tmp[i]], p[tmp[j]]);
55             if (d3 < d) d = d3;
56         }
57     }
58     return d;
59 } 
60 
61 int main() {
62     int n;
63     while (scanf("%d", &n), n) {
64         for (int i=0; i<n; ++i) scanf ("%lf%lf", &p[i].x, &p[i].y);
65         sort(p, p+n, cmp);
66         double ans = closestPair(0, n-1) * 0.5;
67         printf ("%.2lf\n", ans); 
68     }
69     return 0;
70 }
posted on 2012-04-26 20:23 Try86 阅读(248) 评论(0) 收藏举报