Submission #481293

#	Time	Username	Problem	Language	Result	Execution time	Memory
481293		Markadiusz	Kangaroo (CEOI16_kangaroo)	C++17	100 / 100	37 ms	31732 KiB

kangaroo

#include <bits/stdc++.h>
using namespace std;
using LL=long long;
#define FOR(i,l,r) for(int i=(l);i<=(r);++i)
#define REP(i,n) FOR(i,0,(n)-1)
#define ssize(x) int(x.size())
template<class A,class B>auto&operator<<(ostream&o,pair<A,B>p){return o<<'('<<p.first<<", "<<p.second<<')';}
template<class T>auto operator<<(ostream&o,T x)->decltype(x.end(),o){o<<'{';int i=0;for(auto e:x)o<<(", ")+2*!i++<<e;return o<<'}';}
#ifdef DEBUG
#define debug(x...) cerr<<"["#x"]: ",[](auto...$){((cerr<<$<<"; "),...);}(x),cerr<<'\n'
#else
#define debug(...) {}
#endif

int main() {
	cin.tie(0)->sync_with_stdio(0);
	
	const long long mod = 1e9 + 7;
	int n, cs, cf;
	cin >> n >> cs >> cf;
	debug(n, cs, cf);
	if (cs > cf) {
		swap(cs, cf);
	}
	debug(cs, cf);
	vector <vector <long long> >dp(n + 1, vector <long long> (n + 1, 0ll));
	dp[1][1] = 1;
	FOR(i, 1, n - 1) {
		FOR(j, 1, n - 1) {
			if (i + 1 == cs || i + 1 == cf) {
				dp[i + 1][j + 1] = (dp[i + 1][j + 1] + dp[i][j]) % mod;
				dp[i + 1][j] = (dp[i + 1][j] + dp[i][j]) % mod;
			}
			else if (i < cs) {
				dp[i + 1][j + 1] = (dp[i + 1][j + 1] + dp[i][j] * (j + 1)) % mod;
				dp[i + 1][j - 1] = (dp[i + 1][j - 1] + dp[i][j] * (j - 1)) % mod;
			}
			else if (i < cf) {
				dp[i + 1][j + 1] = (dp[i + 1][j + 1] + dp[i][j] * j) % mod;
                                dp[i + 1][j - 1] = (dp[i + 1][j - 1] + dp[i][j] * (j - 1)) % mod;
			}
			else { // i >= cf
				dp[i + 1][j + 1] = (dp[i + 1][j + 1] + dp[i][j] * (j - 1)) % mod;
                                dp[i + 1][j - 1] = (dp[i + 1][j - 1] + dp[i][j] * (j - 1)) % mod;
			}
		}
	}
	debug(dp);
	cout << dp[n][1] << endl;
	
}

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