Submission #723251

#	Time	Username	Problem	Language	Result	Execution time	Memory
723251		n0sk1ll	Boat (APIO16_boat)	C++14	100 / 100	547 ms	464 KiB

boat

#include <bits/stdc++.h>

#define FAST ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);cerr.tie(0)
#define mp make_pair
#define xx first
#define yy second
#define pb push_back
#define pf push_front
#define popb pop_back
#define popf pop_front
#define all(x) x.begin(),x.end()
#define ff(i,a,b) for (int i = a; i < b; i++)
#define fff(i,a,b) for (int i = a; i <= b; i++)
#define bff(i,a,b) for (int i = b-1; i >= a; i--)
#define bfff(i,a,b) for (int i = b; i >= a; i--)

using namespace std;
long double typedef ld;
unsigned int typedef ui;
long long int typedef li;
pair<int,int> typedef pii;
pair<li,li> typedef pli;
pair<ld,ld> typedef pld;
vector<vector<int>> typedef graph;
unsigned long long int typedef ull;
//const int mod = 998244353;
const int mod = 1000000007;







//Note to self: Check for overflow

int inv[2005];

int power(int a, int n)
{
    li c=1;
    while (n)
    {
        if (n&1) (c*=a)%=mod;
        a=(li)a*a%mod,n>>=1;
    }
    return c;
}

int a[505],b[505];

int dp[505];

int main()
{
    FAST;

    int n; cin>>n;
    fff(i,1,n) cin>>a[i]>>b[i];

    vector<int> kords;
    kords.pb(0);
    kords.pb(mod);
    fff(i,1,n) kords.pb(a[i]);
    fff(i,1,n) kords.pb(b[i]+1);
    sort(all(kords));
    kords.erase(unique(all(kords)),kords.end());

    dp[0]=1;
    fff(i,1,2000) inv[i]=power(i,mod-2);
    inv[0]=1;

    ff(k,1,(int)kords.size()-1)
    {
        bfff(i,1,n) if (a[i]<=kords[k] && kords[k]<=b[i])
        {
            li binom=1,gore=kords[k+1]-kords[k],dole=0;
            bfff(f,1,i)
            {
                if (a[f]<=kords[k] && kords[k]<=b[f])
                {
                    (binom*=(gore++))%=mod;
                    (binom*=(inv[++dole]))%=mod;
                }
                (dp[i]+=(li)dp[f-1]*binom%mod)%=mod;
            }
        }

        //cout<<kords[k]<<": ";
        //fff(i,1,n) cout<<dp[i]<<" "; cout<<endl;
    }

    int ans=0;
    fff(i,1,n) (ans+=dp[i])%=mod;
    cout<<ans<<"\n";
}

//Note to self: Check for overflow

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