Настройки поиска

#include<cstdio>
#include<vector>
#include<algorithm>
#include<iostream>
#include<cmath>

using namespace std;

typedef long long ll;
typedef pair<ll,ll> pt;
typedef vector<pt> vpii;

#define x first
#define y second
#define mp make_pair
#define pb push_back

int n;
vpii v;
vector<int> ans;

int cw( pt & p1, pt & p2, pt & p3 ) {
    return (
            ( p1.y + p2.y ) * ( p2.x - p1.x ) + 
            ( p2.y + p3.y ) * ( p3.x - p2.x ) +
            ( p1.y + p3.y ) * ( p1.x - p3.x )
            ) >= 0;
}
int ccw( pt & p1, pt & p2, pt & p3 ) {
    return (
            ( p1.y + p2.y ) * ( p2.x - p1.x ) + 
            ( p2.y + p3.y ) * ( p3.x - p2.x ) +
            ( p1.y + p3.y ) * ( p1.x - p3.x )
            ) <= 0;
}
void out( vpii & v ) {
    for( int i = 0; i < 15; ++i )
        cerr << "-";
    cerr << endl;
    for( int i = 0; i < v.size(); ++i )
        cerr << v[ i ].x << " " << v[ i ].y << endl; 
    for( int i = 0; i < 15; ++i )
            cerr << "-";
        cerr << endl;
} 
int cmp( int a, int b ) {
    return v[ a ] < v[ b ];
}
vpii convex_hull( vpii v ) {
    vector<int> vec;
    for( int i = 0; i < v.size(); ++i )
        vec.pb( i );
    sort( vec.begin(), vec. end(), cmp );
    //out( v );
    pt p1 = v[ vec[ 0 ] ];
    pt p2 = v[ vec[ vec.size() - 1 ] ];
    vpii up, down;
    down.pb( p1 );
    up.pb( p1 );
    vector<int> d, u;
    d.pb( vec[ 0 ] );
    u.pb( vec[ 0 ] );
    for( int i = 1; i < v.size(); ++i ) {
        if( i == v.size() - 1 || cw( p1, v[ vec[ i ] ], p2 ) ) {
            while( up.size() > 1 && ccw( up[ up.size() - 2 ], up[ up.size() - 1 ], v[ vec[ i ] ] ) )
                up.pop_back(),
                u.pop_back();
            up.pb( v[ vec[ i ] ] );
            u.pb( vec[ i ] );
        }
        if( i == v.size() - 1 || ccw( p1, v[ vec[ i ] ], p2 ) ) {
            while( down.size() > 1 && cw( down[ down.size() - 2 ], down[ down.size() - 1 ], v[ vec[ i ] ] ) )
                down.pop_back(),
                d.pop_back();
            down.pb( v[ vec[ i ] ] );
            d.pb( vec[ i ] );
        }
    }
    vpii res;
    for( int i = 0; i < down.size(); ++i )
        res.pb( down[ i ] ),
        ans.pb( d[ i ] );
    for( int i = up.size() - 2; i > 0; --i )
        res.pb( up[ i ] ),
        ans.pb( u[ i ] );
    //out( res );
    return res;
}
double dist( pt & p1, pt & p2 ) {
    return sqrt( ( double )( p1.x - p2.x ) * ( p1.x - p2.x ) +
            ( p1.y - p2.y ) * ( p1.y - p2.y) );
}
ll square( pt & p1, pt & p2 ) {
    return ( p1.y + p2.y ) * ( p2.x - p1.x );
}
int main() {
    freopen( "convex.in", "r", stdin );
    freopen( "convex.out", "w", stdout ); 
    cin >> n;
    v.resize( n );
    for( int i = 0; i < n; ++i )
        cin >> v[ i ].x >> v[ i ].y;
    v = convex_hull( v );
    //out( v );
    cout << v.size() << endl;
    for( int i = 0; i < v.size(); ++i ) 
        cout << ans[ i ] + 1 << " ";
    double per = 0.0;
    ll sq = 0;
    for( int i = 0; i < v.size(); ++i ) {
        int j = ( i + 1 ) % v.size();
        per += dist( v[ i ], v[ j ] );
        sq += square( v[ i ], v[ j ] );
    }
    sq = abs( sq );
    cout.precision( 7 );
    cout << fixed << endl << per << endl;// << -double( sq ) / 2.0 << endl;
    if( sq & 1 )
        cout << sq / 2 << ".500000";
    else cout << sq / 2 << ".000000";
    return 0;
}

cout.precision( 7 );

double dist( pt & p1, pt & p2 ) {
    return sqrt( ( double )( p1.x - p2.x ) * ( p1.x - p2.x ) +
            ( p1.y - p2.y ) * ( p1.y - p2.y) );
}

long double dist( pt & p1, pt & p2 ) {
    return sqrt( ( long double )( p1.x - p2.x ) * ( p1.x - p2.x ) +
            ( p1.y - p2.y ) * ( p1.y - p2.y) );
}