Submission #31096

#	Time	Username	Problem	Language	Result	Execution time	Memory
31096		tatatan	Boat (APIO16_boat)	C++11	100 / 100	1296 ms	5176 KiB

boat

#include <bits/stdc++.h>
#define mp make_pair
#define pb push_back
#define pii pair<int,int>
#define LL long long
#define st first
#define nd second
#define endl '\n'
using namespace std;

const int MAXN=505,mod=1e9+7;
int inverse[MAXN],dp[MAXN][MAXN*3],n,a[MAXN],b[MAXN];
vector<int> v;

void add(int &x,int y) {

	x+=y;
	if(x>=mod)
		x-=mod;

}

int bpow(int x,int y) {

	LL ret=1,t=x;
	while(y) {
		if(y&1)
			ret=(ret*t)%mod;
		y>>=1;
		t=(t*t)%mod;
	}
	return (int)ret;

}

int main() {

	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cin>>n;
	for(int i=1;i<=n;++i) {
		cin>>a[i]>>b[i];
		v.pb(a[i]);
		v.pb(b[i]+1);
		inverse[i]=bpow(i,mod-2);
	}
	v.pb(0);
	sort(v.begin(),v.end());
	v.resize(unique(v.begin(),v.end())-v.begin());
	for(int i=1;i<=n;++i) {
		a[i]=lower_bound(v.begin(),v.end(),a[i])-v.begin();
		b[i]=lower_bound(v.begin(),v.end(),b[i]+1)-v.begin();	
	}
	for(int i=0;i<v.size();++i)
		dp[n+1][i]=1;
	for(int i=n;i>=1;--i) {
		for(int j=v.size()-2;j>=1;--j) {
			add(dp[i][j],dp[i][j+1]);
			if(!(j>=a[i]&&j<b[i]))
				continue;
			LL nCr=1,x=v[j+1]-v[j],y=1;
			for(int k=i;k<=n;++k) {
				if(j>=a[k]&&j<b[k]) {
					nCr=(nCr*x)%mod;
					nCr=(nCr*inverse[y])%mod;
					++x; ++y;
				}
				add(dp[i][j],(nCr*dp[k+1][j+1])%mod);
			}
			//cout<<i<<" "<<j<<" "<<v[j]<<" "<<dp[i][j]<<endl;
		}
	}
	int ans=0;
	for(int i=1;i<=n;++i)
		add(ans,dp[i][1]);
	cout<<ans<< endl;

}

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:54:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<v.size();++i)
               ^

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