Submission #310024

#	Time	Username	Problem	Language	Result	Execution time	Memory
310024		vipghn2003	Boat (APIO16_boat)	C++14	0 / 100	1716 ms	6596 KiB

boat

#include<bits/stdc++.h>
using namespace std;

const int N=505;
const int mod=1e9+7;
int n,l[N],r[N],dp[N][N*2],sum[N][N*2],igt[N],gt[N],ways[N*2][N];

int Power(int x,int n)
{
    if(!n) return 1;
    if(n%2) return 1ll*Power(x,n-1)*x%mod;
    int tmp=Power(x,n/2);
    return 1ll*tmp*tmp%mod;
}

void init()
{
    gt[0]=1;
    for(int i=1;i<=N-5;i++) gt[i]=1ll*gt[i-1]*i%mod;
    igt[N-5]=Power(gt[N-5],mod-2);
    for(int i=N-5-1;i>=0;i--) igt[i]=1ll*igt[i+1]*(i+1)%mod;
}

int C(int k,int n)
{
    if(k<0||k>n) return 0;
    if(n<=500) return 1ll*gt[n]*igt[n-k]%mod*igt[k]%mod;
    int res=igt[k];
    for(int i=n-k+1;i<=n;i++) res=1ll*res*i%mod;
    return res;
}

main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cin>>n;
    init();
    vector<int>val;
    for(int i=1;i<=n;i++)
    {
        cin>>l[i]>>r[i];
        r[i]++;
        val.push_back(l[i]);
        val.push_back(r[i]);
    }
    val.push_back(0);
    sort(val.begin(),val.end());
    val.erase(unique(val.begin(),val.end()),val.end());
    for(int i=1;i<=n;i++)
    {
        l[i]=lower_bound(val.begin(),val.end(),l[i])-val.begin();
        r[i]=lower_bound(val.begin(),val.end(),r[i])-val.begin();
    }
    int sz=val.size()-1;
    for(int i=1;i<=sz-1;i++)
    {
        int cur=C(1,val[i+1]-val[i]);
        for(int k=1;k<=n;k++)
        {
            for(int j=k;j<=n;j++) ways[i][j]=(ways[i][j]+1ll*cur*C(k-1,j-1)%mod)%mod;
            cur=1ll*cur*(n-k)%mod;
            cur=1ll*cur*Power(k+1,mod-2)%mod;
        }
    }
    int res=0;
    dp[0][0]=1;
    for(int j=0;j<=sz-1;j++) sum[0][j]=1;
    for(int i=1;i<=n;i++)
    {
        for(int j=l[i];j<r[i];j++)
        {
            int cnt=0;
            for(int k=i;k>=1;k--)
            {
                if(val[l[k]]<=val[j]&&val[j+1]<=val[r[k]]);
                else cnt++;
                dp[i][j]=(dp[i][j]+1ll*sum[k-1][j-1]*ways[j][i-k+1-cnt]%mod)%mod;
            }
        }
        for(int j=1;j<=sz-1;j++)
        {
            sum[i][j]=(sum[i][j-1]+dp[i][j])%mod;
        }
        res=(res+sum[i][sz-1])%mod;
    }
    cout<<res;
}

Compilation message (stderr)

boat.cpp:33:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
   33 | main()
      |      ^

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