2019-2020nowcoder牛客寒假基础1

#include <cstdio>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <cstring>
#include <queue>
#include <set>
#include <map>
#include <stack>

using namespace std;
#define scd(a) scanf("%d",&a)
#define scdd(a,b) scanf("%d%d",&a,&b)
#define scddd(a,b,c) scanf("%d%d%d",&a,&b,&c)
#define scl(a) scanf("%lld",&a)
#define scll(a,b) scanf("%lld%lld",&a,&b)
#define prl(a) printf("%lld
",a)
#define prd(a) printf("%d
",a)
#define prf(a) printf("%.8lf
",a)
#define ptd(a) printf("%d ",a)
#define scf(a) scanf("%lf",&a)
#define scff(a,b) scanf("%lf%lf",&a,&b)
#define scfff(a,b,c) scanf("%lf%lf%lf",&a,&b,&c)
#define rint register int
#define mem(a) memset(a,0,sizeof(a))
#define rush() int T;scd(T);while(T--)
#define lc(i) (i<<1)
#define rc(i) (i<<1|1)
#define mp make_pair
#define lowbit(x) (x&(-x))
typedef long long ll;
typedef double db;
inline int read() {
    char c=getchar();
    int x=0,f=1;
    while(c<'0'||c>'9') {
        if(c=='-')f=-1;
        c=getchar();
    }
    while(c>='0'&&c<='9') {
        x=x*10+c-'0';
        c=getchar();
    }
    return x*f;
}
const int inf = 2147483647-1;
const db  infdb = 1.78e+308;
const int maxn = 1e5 + 10;
const ll mod = 1e9 + 7;
struct pos{
    int x, y;
}p[maxn], st;
db k(pos a, pos b) {
    return 1.0 * (a.y - b.y) / (a.x - b.x);
}
db m(pos a, pos b) {
    return 1.0 * (a.x - b.x) / (a.y - b.y);
}
bool cmp1(pos &a, pos &b) {
    return a.x < b.x;
}
bool cmp2(pos &a, pos &b) {
    return a.y < b.y;
}
int n, kk;
db solve1() {
    vector<db> v;
    if (st.x > 0) {
        for (int i = 1; i <= n; ++i) {
            if (p[i].x > 0) continue;
            db kx = k(st, p[i]);
            v.push_back(st.y + kx * (0 - st.x));
        }
    } else {
        for (int i = 1; i <= n; ++i) {
            if (p[i].x < 0) continue;
            db kx = k(st, p[i]);
            v.push_back(st.y + kx * (0 - st.x));
        }
    }
    int sz = v.size();
    if (n - sz > kk) return -1;
    sort(v.begin(), v.end());
    db res = infdb;
    int len = min(n - kk, sz);
    for (int i = 0; i <= v.size()-len; ++i) {
        res = min(res, v[i + len - 1] - v[i]);
    }
    return res;
}
db solve2() {
    vector<db> v;
    if (st.y > 0) {
        for (int i = 1; i <= n; ++i) {
            if (p[i].y > 0) continue;
            db my = m(st, p[i]);
            v.push_back(st.x + my * (0 - st.y));
        }
    } else {
        for (int i = 1; i <= n; ++i) {
            if (p[i].y < 0) continue;
            db my = m(st, p[i]);
            v.push_back(st.x + my * (0 - st.y));
        }
    }
    int sz = v.size();
    if (n - sz > kk) return -1;
    sort(v.begin(), v.end());
    db res = infdb;
    int len = min(n - kk, sz);
    for (int i = 0; i <= v.size()-len; ++i) {
        res = min(res, v[i + len - 1] - v[i]);
    }
    return res;
}
int main () {
    st.x = read(), st.y = read();
    n = read(), kk = read();
    for (int i = 1; i <= n; ++i) {
        p[i].x = read();
        p[i].y = read();
    }
    db ans, tmp1 = solve1(), tmp2 = solve2();
    if (tmp1 == -1) {
        prf(tmp2);
    }
    else if (tmp2 == -1)
        prf(tmp1);
    else
        prf(min(tmp1, tmp2));
    return 0;
}