#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 << '}'; } ostream& operator<<(ostream &o, string &s) { return o << s.data(); } #ifdef DEBUG #define debug(x...) cerr << "[" #x "]: ", [](auto... $) {((cerr << $ << "; "), ...); }(x), cerr << '\n' #else #define debug(...) {} #endif const int MAXN = 3003; LL dp[MAXN][MAXN][2]; int main() { cin.tie(0)->sync_with_stdio(0); int n, k; constexpr LL mod = (LL) (1e9 + 7); cin >> n >> k; dp[0][0][0] = 1; FOR(i, 1, n) { FOR(j, 1, i) { dp[i][j][0] = (dp[i - 1][j][0] + dp[i - 1][j][1]) * (LL) (j); dp[i][j][0] %= mod; dp[i][j][1] = dp[i - 1][j - 1][0] * (LL) (k - j + 1) + dp[i - 1][j][1] * (LL) (k - j); dp[i][j][1] %= mod; } } LL ans = 0; FOR(i, 1, n) { ans += dp[n][i][0]; ans %= mod; } cout << ans << '\n'; return 0; }
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 | #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 << '}'; } ostream& operator<<(ostream &o, string &s) { return o << s.data(); } #ifdef DEBUG #define debug(x...) cerr << "[" #x "]: ", [](auto... $) {((cerr << $ << "; "), ...); }(x), cerr << '\n' #else #define debug(...) {} #endif const int MAXN = 3003; LL dp[MAXN][MAXN][2]; int main() { cin.tie(0)->sync_with_stdio(0); int n, k; constexpr LL mod = (LL) (1e9 + 7); cin >> n >> k; dp[0][0][0] = 1; FOR(i, 1, n) { FOR(j, 1, i) { dp[i][j][0] = (dp[i - 1][j][0] + dp[i - 1][j][1]) * (LL) (j); dp[i][j][0] %= mod; dp[i][j][1] = dp[i - 1][j - 1][0] * (LL) (k - j + 1) + dp[i - 1][j][1] * (LL) (k - j); dp[i][j][1] %= mod; } } LL ans = 0; FOR(i, 1, n) { ans += dp[n][i][0]; ans %= mod; } cout << ans << '\n'; return 0; } |