Linerarity(P2780)

这个可以先排好序，然后计算出的后面的点的关系与前面的点的已经没有关系，既然有关系前面的点已经计算过。然后排好序（这里不会费多少时间的）找出有多少共线即可。

#include<iostream>#include<cstdio>#include<algorithm>#include<queue>#include<vector>#include<cmath>#include<set>#include<map>using namespace std;#define N 1001struct my{int x,y;bool operator<(my a){if (a.x==x)return a.y<y;else return a.x<x;}}go[N];double cc(my a,my b){if (a.x==b.x)return 100000000;return (double)(b.y-a.y)/(double)(b.x-a.x);}int n;double cur[N*N];int main(){int i,j,k;while (cin>>n){for (i=0;i<n;i++)scanf("%d%d",&go[i].x,&go[i].y);sort(go,go+n);int l;int ans=2;for (i=0;i<n-1;i++){l=0;for (j=i+1;j<n;j++){double temp=cc(go[i],go[j]);cur[l++]=temp;}sort(cur,cur+l);int num=0;//cout<<l<<endl;for (j=1;j<l;j++){num=2;//cout<<cur[j-1]<<' '<<cur[j]<<' '<<cur[j-1]-cur[j]<<endl;while (j<l&&fabs(cur[j-1]-cur[j])<=1e-6)num++,j++;ans=max(ans,num);}}cout<<ans<<endl;}return 0;}

Linearity

Time Limit: 3000MS Memory Limit: 65536KTotal Submissions: 6965 Accepted: 1578

Description

Alice often examines star maps where stars are represented by points in a plane and there is a Cartesian coordinate for each star. Let the Linearity of a star map be the maximum number of stars in a straight line.

For example, look at the star map shown on the figure above, the Linearity of this map is 3, because the star 1, star 2, and star 5 are within the same straight line, and there is no straight line that passes 4 stars.

You are to write a program to find the Linearity of a star map.

Input

Input will contain multiple test cases. Each describes a star map.

For each test case, the first line of the input contains the number of stars N (2 <= N <= 1000). The following N lines describe coordinates of stars (two integers X and Y per line separated by a space, 0 <= X, Y <= 1000). There can be only one star at one point of the plane.

Output

Output the Linearity of the map in a single line.

Sample Input

50 02 00 21 12 2

Sample Output

3

Source