Mr. Main and Windmills 模拟，计算几何（昆明）

• $O(nmlogn)$，这么一算都1e8了
• long double，但好像double也可以过

#include <iostream>
#include <algorithm>
#include <cstring>
#include <queue>
#include <vector>
#define debug(a) cout << #a << " = " << a << endl;
//#define x first
//#define y second
#define LD long double
using namespace std;
typedef long long ll;

const int N = 1005;
const double INF = 1e9 + 7;

struct point
{
    
    
    LD x, y;
}A[N], stk[N];

LD slope(point s, point t)
{
    
    
    if (s.x == t.x)
        return INF;
    return (t.y - s.y) / (t.x - s.x);
}

struct line
{
    
    
    LD k, b;
    point fromP, endP;
    
    line(){
    
    }
    line(point s, point t)
    {
    
    
        fromP = s, endP = t;
        
        k = slope(s, t);
        if (k == INF) b = INF;
        else b = s.y - k * s.x;
    }
};

point findPoint(line a, line b)
{
    
    
    if (a.k == b.k)
        return point{
    
    INF, INF};
    
    LD xpos, ypos;
    
    if (a.k == INF)
        xpos = a.fromP.x;
    else if (b.k == INF)
        xpos = b.fromP.x;
    else
        xpos = (b.b - a.b) / (a.k - b.k);
    
    if (a.k == 0)
        ypos = a.fromP.y;
    else if (b.k == 0)
        ypos = b.fromP.y;
    else
        ypos = xpos * a.k + a.b;
    
    return point{
    
    xpos, ypos};
}

int getAllPoint(int n, int h, line city)
{
    
    
    int cnt = 0;
    point s = city.fromP, t = city.endP;
    for (int i = 1; i <= n; i ++ )
    {
    
    
        if (i == h) continue;
        
        line now = line(A[i], A[h]);
        
        if (now.k == city.k)
            continue;
        
        point get = findPoint(now, city);
        
        if (get.x < min(s.x, t.x) || get.x > max(s.x, t.x) || get.y < min(s.y, t.y) || get.y > max(s.y, t.y))
            continue;
        
        stk[ ++ cnt] = get;
    }
    return cnt;
}

int main()
{
    
    
    int n, m;
    scanf("%d%d", &n, &m);
    
    point s, t;
    scanf("%LF%LF%LF%LF", &s.x, &s.y, &t.x, &t.y);
    
    line city = line(s, t);
    
    for (int i = 1; i <= n; i ++ )
    {
    
    
        scanf("%LF%LF", &A[i].x, &A[i].y);
    }
    
    for (int i = 1; i <= m; i ++ )
    {
    
    
        int h, k;
        scanf("%d%d", &h, &k);
        
        int len = getAllPoint(n, h, city);
        
        if (k > len)
        {
    
    
            printf("-1\n");
        }
        else
        {
    
    
            if (city.k == 0)
                sort(stk + 1, stk + 1 + len, [](point a, point b){
    
    return a.x < b.x;});
            else
                sort(stk + 1, stk + 1 + len, [](point a, point b){
    
    return a.y < b.y;});
            
            if (s.y > t.y)
                reverse(stk + 1, stk + 1 + len);
            if (city.k == 0 && s.x > t.x)
                reverse(stk + 1, stk + 1 + len);
            
            printf("%.10LF %.10LF\n", stk[k].x, stk[k].y);
        }
    }
    
    return 0;
}