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Submission #163689

#TimeUsernameProblemLanguageResultExecution timeMemory
163689ryanseeKangaroo (CEOI16_kangaroo)C++14
100 / 100
168 ms23120 KiB
#include "bits/stdc++.h" using namespace std; #define FAST ios_base::sync_with_stdio(false); cin.tie(0); #define pb push_back #define eb emplace_back #define ins insert #define ph push #define f first #define s second #define cbr cerr << "hi\n" #define mmst(x, v) memset((x), v, sizeof ((x))) #define siz(x) ((ll)x.size()) #define all(x) (x).begin(), (x).end() #define lbd(x, y) lower_bound(all(x), y) #define ubd(x, y) upper_bound(all(x), y) #define btinpct(x) __builtin_popcountll((x)) mt19937 rng(chrono::steady_clock::now().time_since_epoch().count()); //can be used by calling rng() or shuffle(A, A+n, rng) inline long long rand(long long x, long long y) { return (rng() % (y+1-x)) + x; } //inclusivesss string inline to_string(char c) {string s(1,c);return s;} template<typename T> inline T gcd(T a,T b){ return a==0?b:gcd(b%a,a); } #define ll long long int #define ld long double #define FOR(ii, ss, ee) for(ll ii = (ss); ii <= (ll)(ee); ++ii) #define DEC(ii, ss, ee) for(ll ii = (ss); ii >= (ll)(ee); --ii) typedef pair <ll, ll> pi; typedef pair <ll, pi> spi; typedef pair <pi, pi> dpi; #define LLINF ((long long) 1e18)//1234567890987654321 #define INF 1234567890ll // #define cerr if(0)cout #define MAXN (2003) ll n, cs, cf, mod=1e9+7; ll dp[MAXN][MAXN]; int main() { FAST cin>>n>>cs>>cf; if(n<=2) { cout<<1<<'\n'; return 0; } if(cs > cf) swap(cs, cf); dp[n+1][0]=1; DEC(i, n, 1) FOR(grps, 0, n-i+1) { if(i > cf) dp[i][grps] = ((grps?dp[i+1][grps-1]:0) + dp[i+1][grps+1] * (grps+1) % mod * grps % mod) % mod; else if(i==cf) dp[i][grps] = (dp[i+1][grps] + dp[i+1][grps+1] * (grps+1) % mod) % mod; else if(i>cs) dp[i][grps] = ((grps?dp[i+1][grps-1]:0) + dp[i+1][grps+1] * (((grps+1) * grps % mod + (grps+1))%mod) % mod) % mod; else if(i==cs) dp[i][grps] = (dp[i+1][grps] + dp[i+1][grps+1] * (grps+1) % mod) % mod; else dp[i][grps] = ((grps?dp[i+1][grps-1]:0) + dp[i+1][grps+1] * (((grps+1)*grps%mod+2*(grps+1)%mod)%mod) % mod) % mod; } cout<<dp[2][0]<<'\n'; }
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