二分。。。。
Squares
Time Limit: 3500MS | Memory Limit: 65536K | |
Total Submissions: 14530 | Accepted: 5488 |
Description
A square is a 4-sided polygon whose sides have equal length and adjacent sides form 90-degree angles. It is also a polygon such that rotating about its centre by 90 degrees gives the same polygon. It is not the only polygon with the latter property, however, as a regular octagon also has this property.
So we all know what a square looks like, but can we find all possible squares that can be formed from a set of stars in a night sky? To make the problem easier, we will assume that the night sky is a 2-dimensional plane, and each star is specified by its x and y coordinates.
So we all know what a square looks like, but can we find all possible squares that can be formed from a set of stars in a night sky? To make the problem easier, we will assume that the night sky is a 2-dimensional plane, and each star is specified by its x and y coordinates.
Input
The input consists of a number of test cases. Each test case starts with the integer n (1 <= n <= 1000) indicating the number of points to follow. Each of the next n lines specify the x and y coordinates (two integers) of each point. You may assume that the points are distinct and the magnitudes of the coordinates are less than 20000. The input is terminated when n = 0.
Output
For each test case, print on a line the number of squares one can form from the given stars.
Sample Input
41 0
0 1
1 1
0 0
9
0 0
1 0
2 0
0 2
1 2
2 2
0 1
1 1
2 1
4
-2 5
3 7
0 0
5 2
0
Sample Output
16
1
Source
Rocky Mountain 2004枚举两个点计算另外俩个,二分查找。。。。。
#include <iostream> #include <cstdio> #include <cstring> #include <algorithm> using namespace std; struct node { int x,y; }p[1100],p1,p2; int n,cnt; bool cmp(node a,node b) { if(a.x!=b.x) return a.x<b.x; return a.y<b.y; } bool findp(node a) { int s=0,t=n-1,m; int X=a.x,Y=a.y; while(s<=t) { m=(s+t)/2; if(p if(p else t=m-1; } return false; } int main() { while(scanf("%d",&n)!=EOF&&n) { cnt=0; for(int i=0;i<n;i++) { scanf("%d%d",&p } sort(p,p+n,cmp); for(int i=0;i<n;i++) { for(int j=i+1;j<n;j++) { p1.x=p p2.x=p[j].x+p[j].y-p if(!findp(p1)) continue; if(findp(p2)) cnt++; } } printf("%d ",cnt/2); } return 0; } |