Submission #200685

#	Time	Username	Problem	Language	Result	Execution time	Memory
200685		dimash241	Boat (APIO16_boat)	C++17	9 / 100	2077 ms	2428 KiB

boat

#pragma GCC target("avx2")
#pragma GCC optimize("O3")

# include <x86intrin.h>
# include <bits/stdc++.h>

# include <ext/pb_ds/assoc_container.hpp>
# include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;
 
template<typename T> using ordered_set = tree <T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#define _USE_MATH_DEFINES_
#define ll long long
#define ld long double
#define Accepted 0
#define pb push_back
#define mp make_pair
#define sz(x) (int)(x.size())
#define every(x) x.begin(),x.end()
#define F first
#define S second
#define lb lower_bound
#define ub upper_bound
#define For(i,x,y)  for (ll i = x; i <= y; i ++) 
#define FOr(i,x,y)  for (ll i = x; i >= y; i --)
#define SpeedForce ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0)
// ROAD to...                                                                                                                                                                                                                Red

inline void Input_Output () {
	//freopen(".in", "r", stdin);
   //freopen(".out", "w", stdout);
}

const double eps = 0.000001;
const ld pi = acos(-1);
const int maxn = 1e7 + 9;
const int mod = 1e9 + 7;
const ll MOD = 1e18 + 9;
const ll INF = 1e18 + 123;
const int inf = 2e9 + 11;
const int mxn = 1e6 + 9;
const int N = 6e5 + 123;                                          
const int M = 22;
const int pri = 997;
const int Magic = 2101;

const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, -1, 0, 1};
 
int n;
int dp[505][1010];
int l[505], r[505];
int vv[N], ptr;
ll inv[N];
 
ll bpow (ll a, ll b) {
	ll res = 1;
	while (b > 0) {
		if (b & 1) (res *= a) %= mod;
		(a *= a) %= mod;
		b /= 2;
	}
	return res;
}


ll C(ll n, int k) {
	ll res = inv[k];
	for (int i = 0; i < k; ++i) {
		res *= (n - i);
		res %= mod;
	}

	return res;
}      

int main () {
   	SpeedForce;

	inv[0] = 1;
	for (int i = 1; i < 501;i ++)
		inv[i] = inv[i-1] * bpow(i, mod - 2) % mod;

	cin >> n;

	for (int i = 1; i <= n; ++i) {
		cin >> l[i] >> r[i];
		r[i]++;
		vv[++ptr] = l[i];
		vv[++ptr] = r[i];
	}
	sort(vv + 1, vv + 1 + ptr);
	ptr = unique(vv + 1, vv + 1 + ptr) - vv - 1;
	for (int i = 0; i < ptr; ++i) dp[0][i] = 1;

	for (int i = 1; i <= n; ++i) {
		for (int j = 1; j <= ptr; ++j) if (l[i] <= vv[j] && vv[j] < r[i]) {
			dp[i][j] = (dp[i-1][j-1] * (ll)(vv[j+1] - vv[j])) % mod;
			for (int k = i - 1, cnt = 1; k > 0; --k) if (l[k] <= vv[j] && r[k] > vv[j]) {
				++cnt;
				dp[i][j] = (dp[i][j] + (ll)dp[k-1][j-1] * C(vv[j+1] - vv[j] - 1, cnt));
			}
		}

		dp[i][0] = 1;
		for (int j = 1; j < ptr; ++j)
			dp[i][j] = ((ll)dp[i][j] + dp[i - 1][j] + dp[i][j-1] - dp[i-1][j-1] + mod) % mod;
	}

	cout << (dp[n][ptr-1] - 1 + mod) % mod << '\n';
	return Accepted;
}

// B...a

• Subtask 1: 9 / 9
• Subtask 2: 0 / 22
• Subtask 3: 0 / 27
• Subtask 4: 0 / 42