Language: C++

#include "bits/stdc++.h"
#include<unordered_map>
#include<unordered_set>
#pragma warning(disable:4996)
using namespace std;
using ld = long double;
const ld eps = 1e-14;

/* ??????????????¬ */

#include <complex>

typedef complex<ld> Point;


const ld pi = acos(-1.0);
const ld dtop = pi / 180.;
const ld ptod = 1. / dtop;

namespace std {
	bool operator<(const Point &lhs, const Point &rhs) {
		if (lhs.real() < rhs.real() - eps) return true;
		if (lhs.real() > rhs.real() + eps) return false;
		return lhs.imag() < rhs.imag();
	}
}

// ????????\???
Point input_Point() {
	ld x, y;
	cin >> x >> y;
	return Point(x, y);
}

// ????????????????????????
bool eq(const ld a, const ld b) {
	return (abs(a - b) < eps);
}

// ??????
ld dot(const Point& a, const Point& b) {
	return real(conj(a) * b);
}

// ??????
ld cross(const Point& a, const Point& b) {
	return imag(conj(a) * b);
}

// ??´????????????
class Line {
public:
	Point a, b;
	Line() : a(Point(0, 0)), b(Point(0, 0)) {}
	Line(Point a, Point b) : a(a), b(b) {}
	Point operator[](const int _num)const {
		if (_num == 0)return a;
		else if (_num == 1)return b;
		else {
			assert(false);
			return Point();
		}
	}
};

// ????????????
class Circle {
public:
	Point p;
	ld r;
	Circle() : p(Point(0, 0)), r(0) {}
	Circle(Point p, ld r) : p(p), r(r) {}
};

// ccw
// 1: a,b,c??????????¨???¨?????????????????¶
//-1: a,b,c???????¨???¨?????????????????¶
// 2: c,a,b???????????´???????????¶
//-2: a,b,c???????????´???????????¶
// 0: a,c,b???????????´???????????¶
int ccw(const Point& a, const Point &b, const Point &c) {
	const Point nb(b - a);
	const Point nc(c - a);
	if (cross(nb, nc) > eps) return 1;   // a,b,c??????????¨???¨?????????????????¶
	if (cross(nb, nc) < -eps) return -1; // a,b,c???????¨???¨?????????????????¶
	if (dot(nb, nc) < 0) return 2;       // c,a,b???????????´???????????¶
	if (norm(nb) < norm(nc)) return -2;  // a,b,c???????????´???????????¶
	return 0;                          // a,c,b???????????´???????????¶
}


/* ???????????? */

// ??´?????¨??´??????????????????
bool isis_ll(const Line& l, const Line& m) {
	return !eq(cross(l.b - l.a, m.b - m.a), 0);
}

// ??´?????¨?????????????????????
bool isis_ls(const Line& l, const Line& s) {
	return isis_ll(l, s) &&
		(cross(l.b - l.a, s.a - l.a) * cross(l.b - l.a, s.b - l.a) < eps);
}

// ????????¨?????????????????????
bool isis_ss(const Line& s, const Line& t) {
	return ccw(s.a, s.b, t.a) * ccw(s.a, s.b, t.b) <= 0 &&
		ccw(t.a, t.b, s.a) * ccw(t.a, t.b, s.b) <= 0;
}

// ????????´????????????
bool isis_lp(const Line& l, const Point& p) {
	return (abs(cross(l.b - p, l.a - p)) < eps);
}

// ?????????????????????
bool isis_sp(const Line& s, const Point& p) {
	return (abs(s.a - p) + abs(s.b - p) - abs(s.b - s.a) < eps);
}

// ??????????¶?
Point proj(const Line &l, const Point& p) {
	ld t = dot(p - l.a, l.b - l.a) / norm(l.a - l.b);
	return l.a + t * (l.b - l.a);
}

//???????±??????????????????????
Point reflect(const Line &l, const Point &p) {
	Point pr = proj(l, p);
	return pr * 2.l - p;
}

// ??´?????¨??´????????????
Point is_ll(const Line &s, const Line& t) {
	Point sv = s.b - s.a, tv = t.b - t.a;
	assert(cross(sv, tv) != 0);
	return s.a + sv * cross(tv, t.a - s.a) / cross(tv, sv);
}
// ??´?????¨??´????????????
vector<Point> is_ll2(const Line &s, const Line& t) {
	Point sv = s.b - s.a, tv = t.b - t.a;
	if (cross(sv, tv) != 0)return vector<Point>(1, is_ll(s, t));
	else {
		vector<Point>ans;
		for (int k = 0; k < 2; ++k) {
			if (isis_sp(s, t[k]) && find(ans.begin(), ans.end(), t[k]) == ans.end())ans.push_back(t[k]);
			if (isis_sp(t, s[k]) && find(ans.begin(), ans.end(), s[k]) == ans.end())ans.push_back(s[k]);
		}
		return ans;
	}
}
// ????????¨???????????????
//???????????£????????¨???????????¨assert(false)
Point is_ss(const Line &s, const Line& t) {
	if (isis_ss(s, t)) {
		for (int k = 0; k < 2; ++k) {
			for (int l = 0; l < 2; ++l) {
				if (s[k] == t[l])return s[k];
			}
		}
		return is_ll(s, t);
	}
	else {
		//??????isis_ss?????????
		assert(false);
		return Point(0, 0);
	}
}
// ????????¨???????????????
vector<Point> is_ss2(const Line &s, const Line& t) {
	vector<Point> kouho(is_ll2(s, t));
	vector<Point>ans;
	for (auto p : kouho) {
		if (isis_sp(s, p) && isis_sp(t, p))ans.emplace_back(p);
	}
	return ans;
}
// ??´?????¨???????????¢
ld dist_lp(const Line& l, const Point& p) {
	return abs(p - proj(l, p));
}

//??´?????¨??´???????????¢
ld dist_ll(const Line& l, const Line& m) {
	return isis_ll(l, m) ? 0 : dist_lp(l, m.a);
}

// ??´?????¨??????????????¢
ld dist_ls(const Line& l, const Line& s) {
	return isis_ls(l, s) ? 0 : min(dist_lp(l, s.a), dist_lp(l, s.b));
}

// ????????¨???????????¢
ld dist_sp(const Line& s, const Point& p) {
	Point r = proj(s, p);
	return isis_sp(s, r) ? abs(r - p) : min(abs(s.a - p), abs(s.b - p));
}

// ????????¨??????????????¢
ld dist_ss(const Line& s, const Line& t) {
	if (isis_ss(s, t)) return 0;
	return min({ dist_sp(s, t.a), dist_sp(s, t.b), dist_sp(t, s.a), dist_sp(t, s.b) });
}


int main() {
	
	int N, M, X, Y; cin >> N >> M >> X >> Y;
	vector<Line>ls;
	vector<Point>ps(1,Point(X,Y));
	vector<int>ids(1, -1);
	vector<Point>foods;
	for (int i = 0; i < N; ++i) {
		int px, py; cin >> px >> py;
		foods.push_back(Point(px, py));
	}
	vector<int>caneats(N, true);
	ld sum = 0;
	vector<ld>p_diss(N,1e18);
	vector<ld>l_diss(N,1e18);

	for (int i = 0; i < M; ++i) {
		pair<ld, int>next(1e18,0);
		for (int j = 0; j < foods.size(); ++j) {
			if (caneats[j]) {

				auto f(foods[j]);
				ld dis = diss[j];
				if (!ps.empty()) {
					auto p(ps.back());
					dis = min(dis, abs(p - f));
				}
				
				if(!ls.empty()){
					auto l(ls.back());
					dis = min(dis, dist_sp(l,f));
				}
				diss[j] = dis;
				next = min(next, make_pair(dis+j*1e-12, j));
			}
		} 
		{
			auto f(foods[next.second]);
			pair<ld, int>connect(1e18,0);
			for (int j = 0; j < ps.size(); ++j) {
				connect = min(connect, make_pair(abs(f - ps[j]) + ids[j]*1e-12, j));
			}
			sum += connect.first;
			Line l{ f,ps[connect.second] };
			ls.push_back(l);
			ps.push_back(f);
			ids.push_back(next.second);
			caneats[next.second] = false;
		}
		
	}
	cout << fixed<<setprecision(10)<<sum << endl;
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:228:42: error: 'diss' was not declared in this scope; did you mean 'dis'?
  228 |                                 ld dis = diss[j];
      |                                          ^~~~
      |                                          dis