#include <bits/stdc++.h> using namespace std; #define int long long #define FOR(I, L, R) for(int I(L) ; I <= (int)R ; ++I) #define FOD(I, R, L) for(int I(R) ; I >= (int)L ; --I) #define FOA(I, A) for(auto &I : A) #define print(A,L,R) FOR(OK, L, R){if(A[OK]<=-oo / 10||A[OK]>=oo)cout<<"- ";else cout<<A[OK]<<' ';}cout<<'\n'; #define prints(A) FOA(OK, A){cout<<OK<<' ';}cout << '\n'; #define printz(A,L,R) FOR(OK, 0, L){FOR(KO, 0, R){if(A[OK][KO]>-oo&&A[OK][KO]<oo)cout<<A[OK][KO]<<' ';else cout << "- ";} cout << '\n';}cout << '\n'; #define fs first #define sd second #define ii pair<int,int> #define iii pair<int, ii> #define all(A) A.begin(), A.end() #define quickly ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); #define FILE "RAUMA" const int N = 3000 + 5; const int mod = 1e9 + 7; const int inv = (mod + 1) / 2; const int oo = 1e18; struct Modint{ int x; Modint(){x = 0;} Modint(int _x){ x = (_x % mod + mod) % mod; } inline Modint operator + (const Modint &other) const{ return (x + other.x) % mod; } inline Modint operator - (const Modint &other) const{ return (x - other.x + mod) % mod; } inline Modint operator * (const Modint &other) const{ return (1LL * x * other.x) % mod; } inline void operator += (const Modint &other){ *this = *this + other; } inline void operator -= (const Modint &other){ *this = *this - other; } inline void operator *= (const Modint &other){ *this = *this * other; } friend ostream& operator << (ostream& os, const Modint &t){ return os << t.x; } }; int n, m; Modint dp[N][N]; signed main(){ quickly if(fopen(FILE".inp", "r")){ freopen(FILE".inp", "r", stdin); freopen(FILE".out", "w", stdout); } cin >> n >> m; dp[n][m] = 1; FOD(i, n, 1){ FOD(j, m, 0){ dp[i - 1][j] += dp[i][j]; if(i > 0 && j > 0){ dp[i - 1][j - 1] += dp[i][j] * 4 * j; } if(i > 1 && j > 0){ dp[i - 2][j - 1] += dp[i][j] * j * (i - 1); } if(i > 0 && j > 1){ dp[i - 1][j - 2] += dp[i][j] * j * (j - 1) * inv; } } } Modint ans = 0; FOR(i, 0, m){ ans += dp[0][i]; } cout << ans - 1; }

tents.cpp: In function 'int main()':
tents.cpp:50:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   50 |                 freopen(FILE".inp", "r", stdin);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
tents.cpp:51:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   51 |                 freopen(FILE".out", "w", stdout);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~