Submission #26408

#	Time	Username	Problem	Language	Result	Execution time	Memory
26408		zscoder	Boat (APIO16_boat)	C++14	100 / 100	959 ms	4164 KiB

boat

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define fbo find_by_order
#define ook order_of_key

typedef long long ll;
typedef pair<ll,ll> ii;
typedef vector<int> vi;
typedef long double ld; 
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> pbds;
typedef set<int>::iterator sit;
typedef map<int,int>::iterator mit;
typedef vector<int>::iterator vit;

const int MOD = 1e9 + 7;

int add(int a, int b)
{
	a+=b;
	while(a>=MOD) a-=MOD;
	return a;
}

int mult(int a, int b)
{
	return (a*1LL*b)%MOD;
}

const int N = 501;

int dp[N+1][2*N+1];
vi x;
int l[2*N+1];
int a[N+1];
int b[N+1];
int inv[N*3+1];

ll modpow(ll a, ll b)
{
	ll r=1;
	while(b)
	{
		if(b&1) r=mult(r,a);
		a=mult(a,a);
		b>>=1;
	}
	return r;
}

int main()
{
	ios_base::sync_with_stdio(0); cin.tie(0);
	int n; cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i]>>b[i];
		x.pb(a[i]);
		x.pb(b[i]+1);
	}
	for(int i=1;i<=N*3;i++) inv[i]=modpow(i,MOD-2);
	sort(x.begin(),x.end());
	x.erase(unique(x.begin(),x.end()),x.end());
	for(int i=0;i<x.size();i++)
	{
		if(i==0) l[i]=x[i];
		else l[i]=x[i]-x[i-1];
	}
	for(int i=1;i<=n;i++)
	{
		a[i]=upper_bound(x.begin(),x.end(),a[i])-x.begin();
		b[i]=upper_bound(x.begin(),x.end(),b[i])-x.begin();
	}
	for(int i=0;i<x.size();i++) dp[0][i]=1;
	for(int i=1;i<=n;i++)
	{
		//cerr<<i<<' '<<a[i]<<' '<<b[i]<<'\n';
		for(int j=a[i];j<=b[i];j++)
		{
			dp[i][j]=add(dp[i][j],mult(dp[i-1][j-1],l[j]));
			int cur=l[j]-1; int cnt=1;
			for(int k=i-1;k>0;k--)
			{
				if(a[k]<=j&&j<=b[k])
				{
					cur=mult(cur,l[j]+cnt-1);
					cur=mult(cur,inv[++cnt]);
					dp[i][j]=add(dp[i][j],mult(dp[k-1][j-1],cur));
				}
			}
		}
		dp[i][0]=1;
		for(int j=1;j<x.size();j++)
		{
			dp[i][j]=add(dp[i][j],dp[i-1][j]);
			dp[i][j]=add(dp[i][j],dp[i][j-1]);
			dp[i][j]=add(dp[i][j],MOD-dp[i-1][j-1]);
		}
	}
	int ans=dp[n][int(x.size())-1];
	ans=add(ans,MOD-1);
	cout<<ans<<'\n';
}

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:72:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<x.size();i++)
               ^
boat.cpp:82:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<x.size();i++) dp[0][i]=1;
               ^
boat.cpp:101:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=1;j<x.size();j++)
                ^

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