poj1696

题意：给定一些点，找一条路径，要求经过点最多，并且不能相交。。。

思路：可以用极角排序，但是实际上就是凸包的变形。。套用凸包模板即可。。

code：

/*
  Time:2013-03-26 18:22:16
  State:Accepted
*/
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#include<cstdio>
#include<string>
using namespace std;
struct oo{int x , y , p;};
int M,n;
oo a[1500], pa;

void init(){
     scanf("%d", &n );
     for (int i = 0; i < n; ++i)
           scanf("%d%d%d",&a[i].p, &a[i].x , &a[i].y);
}

bool cmp(const oo a, const oo b){
     if (a.y < b.y || a.y == b.y && a.x < b.x) return true;
     return false;
}

bool cmpx(const oo a, const oo b){
    int x1 = a.x - pa.x;
    int x2 = b.x - pa.x;
    int y1 = a.y - pa.y;
    int y2 = b.y - pa.y;
    if (x1*y2 -x2*y1 >0) return 1;
    if (x1*y2 - x2*y1 == 0 && 
    x1*x1 + y1*y1 < x2*x2 + y2* y2) return 1;
    return 0;
}

void solve(){
     sort(a, a + n, cmp);  
     for (int i = 0; i < n - 1; ++i){
         pa = a[i];
         sort(a + i + 1, a + n, cmpx );
     }
     printf("%d ", n);
     for (int i = 0;  i < n; ++i)
          printf("%d ",a[i].p);
    
 printf("\n");
}

int main(){
    freopen("poj1696.in","r", stdin);
    freopen("poj1696.out","w",stdout);
    scanf("%d",&M);
    while (M--){
       init();
       solve();
    }
    fclose(stdin); fclose(stdout);
}