UVALive - 6955 Finding Lines 随机算法

题目链接：

http://acm.hust.edu.cn/vjudge/contest/126968#problem/F

题意

给你n个点，问是否有>=p/100*n个点共线(p>=20&&p<=100)。

题解

随机枚举两个点，判过这两条直线的点是否满足要求。

代码

include

include

include

include

include

include

include

include

include

include

include

using namespace std;
#define X first
#define Y second
#define mkp make_pair
#define lson (o<<1)
#define rson ((o<<1)|1)
#define mid (l+(r-l)/2)
#define pb(v) push_back(v)
#define sz() size()
#define all(o) (o).begin(),(o).end()
#define clr(a,v) memset(a,v,sizeof(a))
#define bug(a) cout<<#a<<" = "<<a<<endl
#define rep(i,a,b) for(int i=a;i<(b);i++)

typedef long long LL;
typedef vector VI;
typedef pair<int,int> PII;
typedef vector<pair<int,int> > VPII;

const int INF=0x3f3f3f3f;
const LL INFL=0x3f3f3f3f3f3f3f3fLL;
const double eps=1e-8;

//start----------------------------------------------------------------------

const int maxn=1e5+10;
int n;
LL p;
pair<LL,LL> pt[maxn];

LL Cross(pair<LL,LL> p1,pair<LL,LL> p2){
return p1.Xp2.Y-p1.Yp2.X;
}

int main() {
srand((unsigned)time(NULL));
while(scanf("%d",&n)1){
scanf("%lld",&p);
rep(i,0,n) scanf("%lld%lld",&pt[i].X,&pt[i].Y);
int cnt=1000;
bool su=0;
if(n1){
puts("possible"); continue;
}
while(cnt--){
int a=rand()%n,b;
do{ b=rand()%n; }while(b==a);
int sum=0;
rep(i,0,n){
if(i!=a&&i!=b){
if(!Cross(mkp(pt[i].X-pt[a].X,pt[i].Y-pt[a].Y),mkp(pt[i].X-pt[b].X,pt[i].Y-pt[b].Y))){
sum++;
}
}
if((sum+2)100>=pn){
su=1; break;
}
}
if(su) break;
}
if(su) puts("possible");
else puts("impossible");
}
return 0;
}

//end-----------------------------------------------------------------------