Cod sursa(job #2169912)

Utilizator SenibelanMales Sebastian Senibelan Data 14 martie 2018 19:12:32
Problema Infasuratoare convexa Scor 0
Compilator cpp Status done
Runda Arhiva educationala Marime 1.49 kb
#include <cstdio>
 
#include <algorithm>
#include <fstream>
#include <iomanip>
 
using namespace std;
 
#define x first
#define y second
 
typedef pair<double, double> Point;
 
ifstream fin("infasuratoare.in");
ofstream fout("infasuratoare.out");
 
const int MAX_N = 120005;
 
int n;
Point v[MAX_N];
 
Point stack[MAX_N];
int head;
 
void read() {
    fin >> n;
    for (int i = 1; i <= n; ++i)
        fin >> v[i].x >> v[i].y;
}
 
inline double cross_product(const Point& A, const Point& B, const Point& C) {
    return (B.x - A.x) * (C.y - A.y) - (B.y - A.y) * (C.x - A.x);
}
 
inline int cmp(const Point& p1, const Point& p2) {
    return cross_product(v[1], p1, p2) > 0;
}
 
void sort_points() {
    int pos = 1;
    for (int i = 2; i <= n; ++i)
        if (v[i] < v[pos])
            pos = i;
    swap(v[1], v[pos]);
    sort(v + 2, v + n + 1, cmp);
}
 
void convex_hull() {
    sort_points();
 
    stack[1] = v[1];
    stack[2] = v[2];
    head = 2;
    for (int i = 3; i <= n; ++i) {
        while (head >= 2 && cross_product(stack[head - 1], stack[head], v[i]) < 0)
            --head;
        stack[++head] = v[i];
    }
}
 
void write() {
    fout << fixed;
    fout << head << "\n";
    for (int i = 1; i <= head; ++i)
        fout << setprecision(9) << stack[i].x << " " << stack[i].y << "\n";
}
 
int main() {
    read();
    convex_hull();
    write();
}