Submission #257230

#	Time	Username	Problem	Language	Result	Execution time	Memory
257230		NaimSS	Kangaroo (CEOI16_kangaroo)	C++14	100 / 100	60 ms	32384 KiB

kangaroo

#include <bits/stdc++.h>
#define ld long double
#define endl "\n"
#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define pb(x) push_back(x)
#define mp(a,b) make_pair(a,b)
#define ms(v,x) memset(v,x,sizeof(v))
#define all(v) v.begin(),v.end()
#define ff first
#define ss second
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define per(i, a, b) for(int i = b-1; i>=a ; i--)
#define trav(a, x) for(auto& a : x)
#define allin(a , x) for(auto a : x)
#define td(v) v.begin(),v.end()
#define sz(v) (int)v.size()
//#define int long long
using namespace std;
typedef vector<int> vi;
#define y1 abacaba
#define left sefude
#define db(x) cerr << #x <<" == "<<x << endl;
#define db2(x,y) cerr<<#x <<" == "<<x<<", "<<#y<<" == "<<y<<endl;
typedef long long ll;
typedef pair<int,int> pii;
inline ll mod(ll n, ll m ){ ll ret = n%m; if(ret < 0) ret += m; return ret; }
ll gcd(ll a, ll b){return (b == 0LL ? a : gcd(b, a%b));}
ll exp(ll a,ll b,ll m){
    if(b==0LL) return 1LL;
    if(b==1LL) return mod(a,m);
    ll k = mod(exp(a,b/2,m),m);
    if(b&1LL){
        return mod(a*mod(k*k,m),m);
    }
    else return mod(k*k,m);
}

int n;

const int N = 2020;
const int M = 1e9 + 7;
ll dp[N][N];
int cs,cf;

ll C(int j){
  return (1ll*j*(j-1)/2)%M;
}

ll solve(int i,int j){// to em i em tem j componentes
  if(j < 0)return 0;
  ll &x = dp[i][j];
  
  if(x!=-1)return x;
  
  x = 0;
  int bad = (i>=cs) + (i>=cf);
  if(i == n + 1){
    return x = (j == 1);
  }

  if(i == cs || i == cf){
    return x = (solve(i+1,j) + solve(i+1,j+1))%M;
  }

  // tem j+1 gaps pra criar um cara, mas n pode usar o start/end
  x = (x + 1ll*solve(i+1,j+1)*(j + 1 - bad))%M;  
  // pode juntar o (1,2) ou (2,3) ... (j-1,j)
  x = (x + solve(i+1,j-1)*(j-1));

  return mod(x,M);
}

int32_t main(){
  fastio;
  cin >> n;
  cin >> cs >> cf;
  ms(dp,-1);
  cout << solve(2,1) << endl;
  // math -> gcd it all
  // Did u check N=1? Did you switch N,M?
}

• Subtask 1: 6 / 6
• Subtask 2: 30 / 30
• Subtask 3: 15 / 15
• Subtask 4: 49 / 49