Submission #1213633

#	Time	Username	Problem	Language	Result	Execution time	Memory
1213633		loom	Boat (APIO16_boat)	C++20	100 / 100	1058 ms	8444 KiB

boat

#include<bits/stdc++.h>
using namespace std;
#define int long long
#define inf 5e18
#define nl '\n'
 
const int mod = 1e9+7;

int exp(int a, int b = mod-2){
   int p = 1;  
   while(b > 0){
      if(b % 2) p = p * a % mod;
      a = a * a % mod;
      b /= 2;
   }
   return p;
}

const int N = 2005;
int dp[N][N];

inline void solve(){
   int n;
   cin>>n;
   vector<pair<int,int>> ab(n+1), lr;
   map<int,int> mp;

   for(int i=1; i<=n; i++){
      int a, b;
      cin>>a>>b;
      ab[i] = {a, b};
      mp[a]++;
      mp[b]++;
   }

   int prev = -1;
   lr.push_back({0, 0});

   for(auto [x, c] : mp){
      if(prev != -1 and prev+1 <= x-1) lr.push_back({prev+1, x-1});
      lr.push_back({x, x});

      prev = x;
   }

   int m = lr.size()-1;
   for(int i=0; i<=m; i++) dp[0][i] = 1;

   int fact[n+1], inv[n+1];
   fact[0] =  inv[0] = 1;
   for(int i=1; i<=n; i++) fact[i] = fact[i-1] * i % mod, inv[i] = exp(fact[i]);

   for(int i=1; i<=n; i++){
      auto [a, b] = ab[i];
      dp[i][0] = 1;

      for(int j=1; j<=m; j++){
         auto [l, r] = lr[j];
         int len = r-l+1;
         dp[i][j] = dp[i][j-1];

         int cnt = 0, p = 1;
         for(int k=i; k>0; k--){
            auto [a, b] = ab[k];
            if(l < a or r > b) continue;
            cnt++;
            
            p = p * (len + cnt - 1) % mod;
            dp[i][j] += p * inv[cnt] % mod * dp[k-1][j-1];
            dp[i][j] %= mod;
         }
      }
   }

   cout<<(dp[n][m]-1+mod) % mod<<nl;
}

signed main(){
   ios_base::sync_with_stdio(0);
   cin.tie(NULL);cout.tie(NULL);

   int t = 1;
   //cin>>t;
   while(t--) solve();

   return 0;
}

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