제출 #878417

#제출 시각아이디문제언어결과실행 시간메모리
878417pemguimn캥거루 (CEOI16_kangaroo)C++14
100 / 100
15 ms23132 KiB
#include <bits/stdc++.h> #define int long long #define pii pair<int, int> #define pb push_back #define gcd __gcd #define endl "\n" #define task "hihi" using namespace std; const int N = 2e3 + 5, MOD = 1e9 + 7; int dp[N][N]; signed main(){ ios_base::sync_with_stdio(0); cin.tie(0); //freopen(task".inp", "r", stdin); //freopen(task".out", "w", stdout); int n, cs, cf; cin >> n >> cs >> cf; dp[1][1] = 1; for(int i = 1; i < n; i++){ for(int j = 1; j <= i; j++){ if(i + 1 == cs || i + 1 == cf){ (dp[i + 1][j] += dp[i][j]) %= MOD; (dp[i + 1][j + 1] += dp[i][j]) %= MOD; } else{ (dp[i + 1][j - 1] += dp[i][j] * (j - 1)) %= MOD; (dp[i + 1][j + 1] += dp[i][j] * (j + 1 - (i + 1 > cs) - (i + 1 > cf))) %= MOD; } } } cout << dp[n][1]; return 0; }
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