제출 #759871

#제출 시각아이디문제언어결과실행 시간메모리
759871Asamai캥거루 (CEOI16_kangaroo)C++17
0 / 100
1 ms340 KiB
#include <bits/stdc++.h> using namespace std; template<class A, class B> bool maximize(A& x, B y) {if (x < y) return x = y, true; else return false;} template<class A, class B> bool minimize(A& x, B y) {if (x > y) return x = y, true; else return false;} #define all(a) a.begin(), a.end() #define pb push_back #define pf push_front #define fi first #define se second // #define int long long typedef long long ll; typedef unsigned long long ull; typedef double db; typedef long double ld; typedef pair<db, db> pdb; typedef pair<ld, ld> pld; typedef pair<int, int> pii; typedef pair<ll, ll> pll; typedef pair<ll, int> plli; typedef pair<int, ll> pill; const int MAX_N = 2e3 + 5; const int mod = 1e9 + 7; // 998244353 int n, s, t; int dp[MAX_N][MAX_N]; signed main() { ios_base::sync_with_stdio(false); cin.tie(nullptr); cin >> n >> s >> t; dp[1][1] = 1; int cnt = 0; for (int i = 1; i < n; i++) { for (int j = 1; j <= i; j++) { if (!dp[i][j]) continue; if (i + 1 == s || i + 1 == t) { // tao ra 1 tplt rieng (dp[i + 1][j + 1] += dp[i][j]) %= mod; // ghep vao 1 tplt (dp[i + 1][j] += dp[i][j]) %= mod; } else { // tao ra 1 tplt rieng -> j + 1 - cnt vi tri if (j + 1 - cnt > 0) { (dp[i + 1][j + 1] += 1ll * dp[i][j] * (j + 1 - cnt) % mod) %= mod; } // ket noi 2 tlpt nao do -> j - 1 vi tri (dp[i + 1][j - 1] += 1ll * dp[i][j] * (j - 1) % mod) %= mod; } } if (i == s || i == t) cnt++; } cout << dp[n][1]; return 0; } /* */
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