/*###############################################################################################################
## Author : Kim Tae Yoon (Serendipity__) ##
###############################################################################################################*/
#include <bits/stdc++.h>
#define fastio std::ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define prntyes cout<<"Yes\n";
#define prntno cout<<"No\n";
using namespace std;
#ifndef ONLINE_JUDGE
#include "___debug.h"
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif
// mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count()); // random int64 generator
typedef long long ll;
typedef unsigned long ul;
typedef unsigned long long ull;
typedef __int128 ll128;
typedef long double ld;
typedef pair<int, int> pi;
typedef pair<ll, ll> pii;
typedef complex<double> inum;
// Macros from KACTL pdf
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef vector<int> vi;
typedef vector<double> vd;
const double PI = acos(-1);
const int INF = 0x3f3f3f3f;
const ll LLINF = 1000000000000000000LL;
const ll MAX = 200005; // depending on the problem
const ll MOD = 998244353; // depending on the problem
template <class T> int sgn(T x) { return (x > 0) - (x < 0); }
template<class T>
struct Point {
typedef Point P;
T x, y;
explicit Point(T x=0, T y=0) : x(x), y(y) {}
bool operator<(P p) const { return tie(x,y) < tie(p.x,p.y); }
bool operator==(P p) const { return tie(x,y)==tie(p.x,p.y); }
P operator+(P p) const { return P(x+p.x, y+p.y); }
P operator-(P p) const { return P(x-p.x, y-p.y); }
P operator*(T d) const { return P(x*d, y*d); }
P operator/(T d) const { return P(x/d, y/d); }
T dot(P p) const { return x*p.x + y*p.y; }
T cross(P p) const { return x*p.y - y*p.x; }
T cross(P a, P b) const { return (a-*this).cross(b-*this); }
T dist2() const { return x*x + y*y; }
double dist() const { return sqrt((double)dist2()); }
// angle to x-axis in interval [-pi, pi]
double angle() const { return atan2(y, x); }
P unit() const { return *this/dist(); } // makes dist()=1
P perp() const { return P(-y, x); } // rotates +90 degrees
P normal() const { return perp().unit(); }
// returns point rotated 'a' radians ccw around the origin
P rotate(double a) const {
return P(x*cos(a)-y*sin(a),x*sin(a)+y*cos(a)); }
friend ostream& operator<<(ostream& os, P p) {
return os << "(" << p.x << "," << p.y << ")"; }
};
typedef Point<ll> P;
void solve() {
ll N; cin>>N;
vector<P> A(N);
for (int i=0;i<N;i++){
ll x,y; cin>>x>>y;
A[i] = P(x,y);
}
int s = 0;
for (int i=1;i<N;i++){
if (A[i].y < A[s].y){
s = i;
}
}
swap(A[0],A[s]);
sort(A.begin()+1, A.end(), [&](P l, P r){
if ((l-A[0]).cross(r-A[0]) == 0){
return (l-A[0]).dist2() > (r-A[0]).dist2();
}
return (l-A[0]).cross(r-A[0]) > 0;
});
vector<int> dp(N),ne(N,-1),in(N,-1);
for (int j=N-1;j>=1;j--){
dp[j] = 1;
P mn = A[j] - A[0];
int idx = -1;
for (int i=j+1;i<N;i++){
if (mn.cross(A[i]-A[j]) < 0){
if (dp[j] < dp[i]+1){
dp[j] = dp[i]+1;
ne[j] = i;
in[j] = idx;
}
}
if (mn.cross(A[i]-A[j]) > 0){
mn = A[i]-A[j];
idx = i;
}
}
}
vector<P> res;
res.push_back(A[0]);
int u = max_element(dp.begin(), dp.end()) - dp.begin();
if (dp[u] <= 1){cout<<0; return;}
cout<<2*dp[u]<<"\n";
while(1){
res.push_back(A[u]);
if (dp[u] == 1){break;}
res.push_back(A[in[u]]);
u = ne[u];
}
for (auto it:res){
cout<<it.x<<" "<<it.y<<"\n";
}
}
int main() {
fastio;
int tc = 1;
// cin >> tc;
while (tc--) {
solve();
}
return 0;
}
Compilation message
footprint.cpp:11:10: fatal error: ___debug.h: No such file or directory
11 | #include "___debug.h"
| ^~~~~~~~~~~~
compilation terminated.
