Submission #79218

#	Time	Username	Problem	Language	Result	Execution time	Memory
79218		qkxwsm	Triangles (CEOI18_tri)	C++14	100 / 100	1638 ms	68812 KiB

tri

/*
    _____
  .'     '.
 /  0   0  \
|     ^     |
|  \     /  |
 \  '---'  /
  '._____.'
*/
#pragma GCC optimize ("O3")
#pragma GCC target ("sse4")
#include "trilib.h"
#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/rope>

using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;

template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
random_device(rd);
mt19937 rng(rd());

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);
}
long long expo(long long a, long long e, long long mod)
{
	return ((e == 0) ? 1 : ((expo(a * a % mod, e >> 1, mod)) * ((e & 1) ? a : 1) % mod));
}
template<class T, class U>
T nmod(T &x, U mod)
{
	if (x >= mod) x -= mod;
}
template<class T>
T gcd(T a, T b)
{
	return (b ? gcd(b, a % b) : a);
}
template<class T>
T randomize(T mod)
{
	return (uniform_int_distribution<T>(0, mod - 1))(rng);
}

#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;
#define sz(x) ((int) (x.size()))

const long double PI = 4.0 * atan(1.0);
const long double EPS = 1e-9;

#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, Q;
rope<int> hull;
int ans;
map<int, bool> mp[MAXN];

bool ccw(int u, int v, int w)
{
	int x = u, y = v, z = w;
	if (v < u && v < w)
	{
		u = y; v = z; w = x;
	}
	else if (w < u && w < v)
	{
		u = z; v = x; w = y;
	}
	if (mp[u].find(v * N + w) != mp[u].end())
	{
		return mp[u][v * N + w];
	}
	Q++;
	if (Q == 1000001) exit(0);
	bool res = !(is_clockwise(u + 1, v + 1, w + 1));
	mp[u][v * N + w] = res; mp[u][w * N + v] = !res;
	return res;
}
int fetch(int idx)
{
	int S = sz(hull);
	return hull[(idx + S) % S];
}
void debug_hull()
{
	cerr << "hull has:";
	for (int x : hull)
	{
		cerr << ' ' << x;
	}
	cerr << endl;
}
void ins2(int i)
{
	assert(sz(hull) == 2);
	int u = hull[0], v = hull[1];
	hull.erase(0, sz(hull));
	if (ccw(u, v, i))
	{
		hull.PB(u); hull.PB(v); hull.PB(i);
	}
	else
	{
		hull.PB(u); hull.PB(i); hull.PB(v);
	}
}

int32_t main()
{
	ios_base::sync_with_stdio(0);
	// cout << fixed << setprecision(10);
	// cerr << fixed << setprecision(10);
	// freopen ("file.in", "r", stdin);
	// freopen ("file.out", "w", stdout);
	N = get_n();
	for (int i = 0; i < N; i++)
	{
		if (sz(hull) <= 1)
		{
			hull.PB(i);
			continue;
		}
		if (sz(hull) == 2)
		{
			ins2(i);
			continue;
		}
		int lo = 0, hi = sz(hull) - 1;
		while(hi > lo)
		{
			int mid = (lo + hi + 1) / 2, idx = fetch(mid);
			if (ccw(fetch(0), idx, i))
			{
				lo = mid;
			}
			else
			{
				hi = mid - 1;
			}
		}
		int idx = lo;
		while(true)
		{
			if (sz(hull) <= 2)
			{
				break;
			}
			if (!ccw(fetch(idx - 1), fetch(idx), i))
			{
				hull.erase(idx, 1);
				idx--;
				if (idx < 0) idx += sz(hull);
			}
			else if (!ccw(i, fetch(idx + 1), fetch(idx + 2)))
			{
				hull.erase((idx + 1 + sz(hull)) % sz(hull), 1);
			}
			else
			{
				break;
			}
		}
		if (sz(hull) == 2)
		{
			ins2(i);
		}
		else if (ccw(fetch(idx), i, fetch(idx + 1)))
		{
			hull.insert(idx + 1, i);
		}
	}
	ans = sz(hull);
	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: 20 / 20
• Subtask 4: 20 / 20
• Subtask 5: 25 / 25