Submission #1066306

#	Time	Username	Problem	Language	Result	Execution time	Memory
1066306		Serendipity__	공룡 발자국 (KOI18_footprint)	C++17	100 / 100	802 ms	114004 KiB

footprint

/*###############################################################################################################
##                                    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;
// 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;

int dp[2][3005][3005];
int track[2][3005][3005];

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]);
    ll dx,dy;
    dx = A[0].x;
    dy = A[0].y;
    for (int i=0;i<N;i++){
        A[i].x -= dx;
        A[i].y -= dy;
    }

    sort(A.begin()+1, A.end(), [&](P l, P r){
        return l.cross(r) > 0;
    });

    for (int j=N-1;j>=1;j--){
        vector<int> L,R;
        for (int i=0;i<N;i++){
            if (A[j].cross(A[i]) > 0){
                L.push_back(i);
            }else if (A[j].cross(A[i]) < 0){
                R.push_back(i);
            }
        }

        sort(L.begin(), L.end(), [&](int l, int r){
            return A[j].cross(A[l],A[r]) > 0;
        });
        sort(R.begin(), R.end(), [&](int l, int r){
            return A[j].cross(A[l],A[r]) > 0;
        });

        int ls = L.size();
        int rs = R.size();
        int p;

        // ccw = 0
        p = 0;
        int mx = -INF;
        int pos = -1;
        for (int t=0;t<rs;t++){
            int i = R[t];
            while(p<ls){
                int k = L[p];
                if (A[j].cross(A[i],A[k]) > 0){
                    if (mx < dp[1][k][j]+1){
                        mx = dp[1][k][j]+1;
                        pos = k;
                    }
                    ++p; 
                }else{
                    break;
                }
            }
            dp[0][j][i] = mx;
            track[0][j][i] = pos;
        }

        // ccw = 1
        p = ls-1;
        mx = 2;
        pos = -1;
        for (int t=rs-1;t>=0;t--){
            int i = R[t];
            while(p>=0){
                int k = L[p];
                if (A[j].cross(A[i],A[k]) < 0){
                    if (mx < dp[0][k][j]+1){
                        mx = dp[0][k][j]+1;
                        pos = k;
                    }
                    --p;
                }else{
                    break;
                }
            }
            dp[1][j][i] = mx;
            track[1][j][i] = pos;
        }
    }

    int ans = 0;
    int s1,s2,t=0;
    for (int i=1;i<N;i++){
        for (int j=i+1;j<N;j++){
            if (dp[0][j][i]+1 > ans){
                ans = dp[0][j][i]+1;
                s1 = j;
                s2 = i;
            }
        }
    }
    if (ans < 4){cout<<0; return;}

    for (int i=0;i<N;i++){
        A[i].x += dx;
        A[i].y += dy;
    }

    cout<<ans<<"\n";
    cout<<A[0].x<<" "<<A[0].y<<"\n";
    cout<<A[s2].x<<" "<<A[s2].y<<"\n";
    while(1){
        if (s1==-1){break;}
        cout<<A[s1].x<<" "<<A[s1].y<<"\n";
        tie(s1,s2) = pi(track[t][s1][s2],s1);
        t^=1;
    }

}

int main() {
    fastio;
    int tc = 1;
    // cin >> tc;
    while (tc--) {
        solve();
    }
    return 0;
}

Compilation message (stderr)

footprint.cpp: In function 'void solve()':
footprint.cpp:178:15: warning: 's2' may be used uninitialized in this function [-Wmaybe-uninitialized]
  178 |     cout<<A[s2].x<<" "<<A[s2].y<<"\n";
      |               ^

• Subtask 1: 14 / 14
• Subtask 2: 12 / 12
• Subtask 3: 29 / 29
• Subtask 4: 45 / 45