Submission #447785

#	Time	Username	Problem	Language	Result	Execution time	Memory
447785		dutch	Boat (APIO16_boat)	C++17	0 / 100	15 ms	8208 KiB

boat

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define valid(x, y) (a[x] <= pts[y] && pts[y+1] <= b[x]+1)

const int MOD = 1e9+7, LIM = 501;

int modInverse(int x){
	int r = 1, p = (MOD - 2) * 2;
	for(int y=x; p/=2; y=(y*y) % MOD)
		if(p & 1) r = (r*y) % MOD;
	return r;
}

int n, a[LIM], b[LIM], dp[LIM][LIM*2], F[LIM], invF[LIM], C[LIM*2][LIM];
vector<int> pts;

signed main(){
	cin.tie(0)->sync_with_stdio(0);

	cin >> n;
	for(int i=0; i<n; ++i){
		cin >> a[i] >> b[i];
		pts.push_back(a[i]);
		pts.push_back(b[i]+1);
	}
	sort(pts.begin(), pts.end());
	pts.resize(unique(pts.begin(), pts.end()) - pts.begin());

	int m = size(pts) - 1, ans = 0;

	F[0] = invF[0] = 1;
	for(int i=1; i<=n; ++i){
		F[i] = (F[i-1] * i) % MOD;
		invF[i] = modInverse(F[i]);
	}
	for(int i=0; i<m; ++i){
		int diff = pts[i+1] - pts[i];
		int p = 1;
		for(int j=1; j<=n; ++j){
			(p *= diff - j + 1) %= MOD;
			C[i][j] = (p * invF[j]) % MOD;
		}
	}

	for(int i=0; i<n; ++i){
		for(int k=0; k<m; ++k){
			if(!valid(i, k)) continue;
			int cnt = 1, p = C[k][1];
			for(int j=i; --j>=0; ){
				if(k) (dp[i][k] += dp[j][k-1] * cnt) %= MOD;
				if(valid(j, k)) p += C[k][++cnt];
			}
			(dp[i][k] += p) %= MOD;
			(ans += dp[i][k]) %= MOD;
		}
		for(int k=1; k<m; ++k) (dp[i][k] += dp[i][k-1]) %= MOD;
	}
	cout << (ans % MOD + MOD) % MOD;
}

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