Submission #72766

#	Time	Username	Problem	Language	Result	Execution time	Memory
72766		qkxwsm	Triangles (CEOI18_tri)	C++17	35 / 100	3061 ms	263168 KiB

tri

/*
    _____
  .'     '.
 /  0   0  \
|     ^     |
|  \     /  |
 \  '---'  /
  '._____.'
*/
#include "trilib.h"
#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>

using namespace std;
using namespace __gnu_pbds;

struct chash
{
	int operator()(int x) const
	{
		x ^= (x >> 20) ^ (x >> 12);
		return x ^ (x >> 7) ^ (x >> 4);
	}
	int operator()(long long x) const
	{
		return x ^ (x >> 32);
	}
};

template<typename T> using orderedset = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename U> using hashtable = gp_hash_table<T, U, chash>;

template<class T>
void readi(T &x)
{
	T input = 0;
	bool negative = false;
	char c = ' ';
	while (c < '-')
	{
		c = getchar();
	}
	if (c == '-')
	{
		negative = true;
		c = getchar();
	}
	while (c >= '0')
	{
		input = input * 10 + (c - '0');
		c = getchar();
	}
	if (negative)
	{
		input = -input;
	}
	x = input;
}
template<class T>
void printi(T output)
{
	if (output == 0)
	{
		putchar('0');
		return;
	}
	if (output < 0)
	{
		putchar('-');
		output = -output;
	}
	int aout[20];
	int ilen = 0;
	while(output)
	{
		aout[ilen] = ((output % 10));
		output /= 10;
		ilen++;
	}
	for (int i = ilen - 1; i >= 0; i--)
	{
		putchar(aout[i] + '0');
	}
	return;
}
template<class T>
void ckmin(T &a, T b)
{
	a = min(a, b);
}
template<class T>
void ckmax(T &a, T b)
{
	a = max(a, b);
}
template<class T, class U>
T normalize(T x, U mod = 1000000007)
{
	return (((x % mod) + mod) % mod);
}
long long randomizell(long long mod)
{
	return ((1ll << 45) * rand() + (1ll << 30) * rand() + (1ll << 15) * rand() + rand()) % mod;
}
int randomize(int mod)
{
	return ((1ll << 15) * rand() + rand()) % mod;
}

#define y0 ___y0
#define y1 ___y1
#define MP make_pair
#define MT make_tuple
#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
#define debug(x) cerr << #x << " = " << x << endl;

const long double PI = 4.0 * atan(1.0);
const long double EPS = 1e-10;

#define MAGIC 347
#define SINF 10007
#define CO 1000007
#define INF 1000000007
#define BIG 1000000931
#define LARGE 1696969696967ll
#define GIANT 2564008813937411ll
#define LLINF 2696969696969696969ll
#define MAXN 40013

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;

int N;
int ans;
int S;
vector<int> hull;
vector<int> arr;
bool flag[MAXN];
hashtable<ll, bool> mp[MAXN];

ll geth(int a, int b)
{
	return 1ll * a * N + b;
}
bool ccw(int u, int v, int w)
{
	if (mp[u].find(geth(v, w)) != mp[u].end())
	{
		return mp[u][geth(v, w)];
	}
	bool res = !(is_clockwise(u + 1, v + 1, w + 1));
	mp[u][geth(v, w)] = res; mp[u][geth(w, v)] = !res;
	mp[v][geth(w, u)] = res; mp[v][geth(u, w)] = !res;
	mp[w][geth(u, v)] = res; mp[w][geth(v, u)] = !res;
	return res;
}
bool cmp(int u, int v)
{
	return !ccw(u, S, v);
}
void get_hull()
{
	sort(arr.begin(), arr.end(), cmp);
	hull.PB(S);
	for (int v : arr)
	{
		while(hull.size() >= 2 && !ccw(hull[hull.size() - 2], hull.back(), v))
		{
			hull.pop_back();
		}
		hull.PB(v);
	}
	return;
}
int find(int u, int v)
{
	// cerr << "find " << u << ' ' << v << endl;
	int net = 0;
	for (int i = 0; i < N; i++)
	{
		if (i == u || i == v) continue;
		if (ccw(u, i, v))
		{
			flag[i] = true;
			net++;
		}
		else
		{
			flag[i] = false;
			net--;
		}
	}
	if (net == N - 2 || net == 2 - N) return u;
	arr.clear();
	S = u;
	for (int i = 0; i < N; i++)
	{
		if (i == u || i == v) continue;
		if ((flag[i] && net <= 0) || (!flag[i] && net > 0))
		{
			arr.PB(i);
		}
	}
	get_hull();
	int rand_idx = randomize(hull.size() - 1);
	u = hull[rand_idx], v = hull[rand_idx + 1];
	hull.clear();
	return find(u, v);
}
int solve()
{
	if (N == 3)
	{
		return 3;
	}
	//find any vertex on the hull
	int u = randomize(N), v = (u + 1 + randomize(N - 1)) % N;
	S = find(u, v);
	arr.clear();
	for (int i = 0; i < N; i++)
	{
		if (S == i) continue;
		arr.PB(i);
	}
	get_hull();
	return hull.size();
}

int32_t main()
{
	ios_base::sync_with_stdio(0);
	srand(time(0));
	// cout << fixed << setprecision(10);
	// cerr << fixed << setprecision(10);
	// if (fopen("input.in", "r"))
	// {
	// 	freopen ("input.in", "r", stdin);
	// 	freopen ("output.out", "w", stdout);
	// }
	N = get_n();
	//find any guy on the hull
	ans = solve();
	give_answer(ans);
	// cerr << "time elapsed = " << (clock() / (CLOCKS_PER_SEC / 1000)) << " ms" << endl;
	return 0;
}

• Subtask 1: 15 / 15
• Subtask 2: 20 / 20
• Subtask 3: 0 / 20
• Subtask 4: 0 / 20
• Subtask 5: 0 / 25