POJ2002 二分查找&哈希

 1 #include <iostream>
 2 #include <cstring>
 3 #include <cstdio>
 4 #include <algorithm>
 5 
 6 using namespace std;
 7 
 8 const int maxn = 1010;
 9 int n;
10 
11 struct node 
12 {
13     int x, y;
14     bool operator <  (const node n) const {
15         if ( x != n.x )
16             return x < n.x;
17         else 
18             return y < n.y;
19     }
20 }star[maxn];
21 
22 bool search(int x, int y)
23 {
24     int low = 0;
25     int high = n;
26     while (low <= high) {
27         int mid = (low + high) / 2;
28         if (star[mid].x == x && star[mid].y == y)
29             return true;
30         else {
31             if (x < star[mid].x || (x == star[mid].x && y < star[mid].y ))
32                 high = mid - 1;
33             else 
34                 low = mid + 1;
35         }
36     }
37     return false;
38 }
39 
40 node s1, s2, s3, s4;
41 
42 void compute(int a, int b)
43 {
44     int xa = star[a].x;
45     int xb = star[b].x;
46     int ya = star[a].y;
47     int yb = star[b].y;
48     s1.x = xa - yb + ya;
49     s1.y = ya + xb - xa;
50     s2.x = xb - yb + ya;
51     s2.y = yb + xb - xa;
52 
53     s3.x = xa + yb - ya;
54     s3.y = ya - xb + xa;
55     s4.x = xb + yb - ya;
56     s4.y = yb - xb + xa;
57 }
58 
59 int main()
60 {
61     while (scanf("%d", &n) && n) {
62         for (int i = 0; i < n; i++) {
63             scanf("%d%d", &star[i].x, &star[i].y);
64         }
65         sort(star, star + n);
66         int ans = 0;
67         for (int i = 0; i < n; i++)
68             for (int j = i + 1; j < n; j++) {
69                 compute(i, j);
70                 if (search(s1.x, s1.y) && search(s2.x, s2.y))
71                     ans++;
72                 if (search(s3.x, s3.y) && search(s4.x, s4.y))
73                     ans++;
74             }
75         ans /= 4;
76         printf("%d\n", ans);
77     }
78     return 0;
79 }