求最远点对，输出距离 

 1 #include<iostream>
 2 #include <math.h>
 3 #include <algorithm>
 4 #include<stdio.h>
 5 
 6 using namespace std;
 7 
 8 #define eps 1e-8
 9 #define zero(x) (((x)>0?(x):-(x))<eps)
10 struct point{ double x, y; }p[100005], convex[100005];
11 
12 double xmult(point p1, point p2, point p0)
13 {
14     return (p1.x - p0.x)*(p2.y - p0.y) - (p2.x - p0.x)*(p1.y - p0.y);
15 }
16 
17 int dist2(point a, point b)
18 {
19     return (a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y);
20 }
21 
22 point p1, p2;
23 int graham_cp(const void* a, const void* b){
24     double ret = xmult(*((point*)a), *((point*)b), p1);
25     return zero(ret) ? (xmult(*((point*)a), *((point*)b), p2) > 0 ? 1 : -1) : (ret > 0 ? 1 : -1);
26 }
27 void _graham(int n, point* p, int& s, point* ch){
28     int i, k = 0;
29     for (p1 = p2 = p[0], i = 1; i<n; p2.x += p[i].x, p2.y += p[i].y, i++)
30     if (p1.y - p[i].y>eps || (zero(p1.y - p[i].y) && p1.x > p[i].x))
31         p1 = p[k = i];
32     p2.x /= n, p2.y /= n;
33     p[k] = p[0], p[0] = p1;
34     qsort(p + 1, n - 1, sizeof(point), graham_cp);
35     for (ch[0] = p[0], ch[1] = p[1], ch[2] = p[2], s = i = 3; i < n; ch[s++] = p[i++])
36     for (; s>2 && xmult(ch[s - 2], p[i], ch[s - 1]) < -eps; s--);
37 }
38 
39 int wipesame_cp(const void *a, const void *b)
40 {
41     if ((*(point *)a).y < (*(point *)b).y - eps) return -1;
42     else if ((*(point *)a).y >(*(point *)b).y + eps) return 1;
43     else if ((*(point *)a).x < (*(point *)b).x - eps) return -1;
44     else if ((*(point *)a).x >(*(point *)b).x + eps) return 1;
45     else return 0;
46 }
47 
48 int _wipesame(point * p, int n)
49 {
50     int i, k;
51     qsort(p, n, sizeof(point), wipesame_cp);
52     for (k = i = 1; i < n; i++)
53     if (wipesame_cp(p + i, p + i - 1) != 0) p[k++] = p[i];
54     return k;
55 }
56 
57 int graham(int n, point* p, point* convex, int maxsize = 1, int dir = 1){
58     point* temp = new point[n];
59     int s, i;
60     n = _wipesame(p, n);
61     _graham(n, p, s, temp);
62     for (convex[0] = temp[0], n = 1, i = (dir ? 1 : (s - 1)); dir ? (i < s) : i; i += (dir ? 1 : -1))
63     if (maxsize || !zero(xmult(temp[i - 1], temp[i], temp[(i + 1) % s])))
64         convex[n++] = temp[i];
65     delete[]temp;
66     return n;
67 }
68 
69 int rotating_calipers(point *ch, int n)
70 {
71     int q = 1, ans = 0;
72     ch[n] = ch[0];
73     for (int p = 0; p < n; p++)
74     {
75         while (xmult(ch[p + 1], ch[q + 1], ch[p]) > xmult(ch[p + 1], ch[q], ch[p]))
76             q = (q + 1) % n;
77         ans = max(ans, max(dist2(ch[p], ch[q]), dist2(ch[p + 1], ch[q + 1])));
78     }
79     return ans;
80 }
81 int main()
82 {
83     int n;
84     cin >> n;
85     for (int i = 0; i < n; i++)
86     {
87         scanf("%lf%lf", &p[i].x, &p[i].y);
88     }
89     int size = graham(n, p, convex, 1, 0);
90     //cout << rotating_calipers(convex, size) << endl;
91     printf("%.8lf\n",sqrt(rotating_calipers(convex, size)));
92     return 0;
93 }

 

posted @ 2013-11-13 20:01  crazy_apple  阅读(461)  评论(0)    收藏  举报