Submission #764509

#	Time	Username	Problem	Language	Result	Execution time	Memory
764509		Ahmed57	Boat (APIO16_boat)	C++17	100 / 100	1453 ms	8308 KiB

boat

#include <bits/stdc++.h>
using namespace std;
long long mod = 1000000007;
long long fast(long long a,long long b){
    if(b==0)return 1;
    if(b==1)return a;
    long long h = fast(a,b/2);h*=h;h%=mod;
    if(b%2==0)return h;
    else return (h*a)%mod;
}
signed main(){
    ios_base::sync_with_stdio(false);cin.tie(0);
    int n;
    cin>>n;
    long long rev[n+1];
    for(int i = 0;i<=n;i++){
        rev[i] = fast(i,mod-2);
    }
    vector<pair<long long,long long>> v;
    vector<long long> ans;
    for(int i = 0;i<n;i++){
        long long x,y;
        cin>>x>>y;
        v.push_back({x,y});
        ans.push_back(x-1);
        ans.push_back(y);
    }
    ans.push_back(0);
    sort(ans.begin(),ans.end());
    ans.resize(unique(ans.begin(),ans.end())-ans.begin());
    long long fin = 0;
    long long dp[2001][501];
    memset(dp,0,sizeof dp);
    long long ps[2001];
    dp[0][0] = 1;
    long long sz = ans.size()+1;
    for(int i = 0;i<=sz+8;i++){
        ps[i] = 1;
    }
    for(int i=1;i<=n;i++){
		int l=lower_bound(ans.begin(),ans.end(),v[i-1].first)-ans.begin();
		int r=lower_bound(ans.begin(),ans.end(),v[i-1].second)-ans.begin();
		for(int j=l;j<=r;j++){
			long long cnt=ans[j]-ans[j-1];
			for(long long h=n;h>=2;h--){
				dp[j][h]=(dp[j][h]+dp[j][h-1]*(cnt-(h-1))%mod*rev[h])%mod;
			}
			dp[j][1]=(dp[j][1]+ps[j-1]*cnt)%mod;
		}
		ps[0]=dp[0][0];
		for(int i=1;i<=sz+9;i++){
			ps[i]=ps[i-1];
			for(int h=0;h<=n;h++){
				ps[i]+=dp[i][h];
			}
			ps[i]%=mod;
		}
	}
    cout<<(ps[sz+8]+(mod-1))%mod<<endl;
}
/*
1 4
3 4
{1,3},{1,4},{2,3},{2,4},{3,4}
*/

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:31:15: warning: unused variable 'fin' [-Wunused-variable]
   31 |     long long fin = 0;
      |               ^~~

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