POJ 2780

A

Time Limit:3000MS  Memory Limit:65536K
Total Submit:55 Accepted:15

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

5
0 0
2 0
0 2
1 1
2 2

 

Sample Output

3

 

Source

错了好几好几次，原因是……哎，应该把i的for循环放在j的外面，被我漏掉了

#include<iostream> #include<math.h> #include<algorithm> using namespace std; #define INF 1e8 #define zero 1e-6 #define M 1001 int n; struct P { int x,y; bool operator<(const P a)const { if(a.x==x) return a.y<y; return a.x<x; } }point[M]; double xielv[M*M/2]; double CalA(P a,P b) { if(b.x==a.x) return INF; double t=(b.y-a.y)*1.0/(b.x-a.x); return t; } int main() { int i,j; while(scanf("%d",&n)!=EOF) { int max=0; for(i=0;i<n;i++) scanf("%d%d",&point[i].x,&point[i].y); sort(point,point+n); int index=0; for(i=0;i<n-1;i++) { index=0; for(j=i+1;j<n;j++) { double t=CalA(point[i],point[j]); xielv[index++]=t; } sort(xielv,xielv+index); int count; for(j=0;j<index-1;j++) { count=2; while(fabs(xielv[j]-xielv[j+1])<=zero) { count++; j++; } max=max>count?max:count; } } printf("%d/n",max); } }