https://codeforc.es/problemset/problem/514/B
题意：与（x0，y0）同一直线的设一枪，最少多少枪全部击倒；
思路：记录全部斜率，找到不同斜率的有多少个；注意k不存在，一开始不存在设为-1，但是斜率会有-1存在=-=，要用一个不存在的数标志；
#include<algorithm> #include<set> #include<queue> #include<cmath> #include<cstring> #include<iostream> #include<set> #include<vector> #include<queue> #include<cmath> #include<cstdio> #include<map> #include<stack> #include<string> #include<bits/stdc++.h> using namespace std; #define sfi(i) scanf("%d",&i) #define pri(i) printf("%d\n",i) #define sff(i) scanf("%lf",&i) #define ll long long #define ull unsigned long long #define mem(x,y) memset(x,y,sizeof(x)) #define INF 0x3f3f3f3f #define eps 1e-16 #define PI acos(-1) #define lowbit(x) ((x)&(-x)) #define zero(x) (((x)>0?(x):-(x))<eps) #define fl() printf("flag\n") #define MOD(x) ((x%mod)+mod)%mod #define endl '\n' #define pb push_back #define lson rt<<1,l,mid #define rson rt<<1|1,mid+1,r #define FAST_IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0) const int maxn=1e6+9; const int mod=1e9+7; inline ll read() { ll f=1,x=0; char ss=getchar(); while(ss<'0'||ss>'9') { if(ss=='-')f=-1;ss=getchar(); } while(ss>='0'&&ss<='9') { x=x*10+ss-'0';ss=getchar(); } return f*x; } double Dis(int x1,int y1,int x2,int y2) { return sqrt((double)(x1-x2)*(x1-x2)+(double)(y1-y2)*(y1-y2)); } double k[maxn]; int main() { //FAST_IO; //freopen("input.txt","r",stdin); int n; double x,y; cin>>n>>x>>y; for(int i=1;i<=n;i++) { double a,b; cin>>a>>b; if(a==x) k[i]=1e9; else { k[i]=(b-y)/(a-x); } //cout<<k[i]<<" "; } //cout<<endl; int ans=1; sort(k+1,k+1+n); for(int i=2;i<=n;i++) { //cout<<k[i]<<" "; if(k[i]-k[i-1]>=eps) ans++; } cout<<ans<<endl; return 0; }
