Submission #114236

#TimeUsernameProblemLanguageResultExecution timeMemory
114236popovicirobertAsceticism (JOI18_asceticism)C++14
100 / 100
34 ms1220 KiB
#include <bits/stdc++.h> #define lsb(x) (x & (-x)) #define ll long long #define ull unsigned long long // 217 // 44 using namespace std; const int MOD = (int) 1e9 + 7; inline int lgput(int a, int b) { int ans = 1; while(b > 0) { if(b & 1) ans = (1LL * ans * a) % MOD; b >>= 1; a = (1LL * a * a) % MOD; } return ans; } const int MAXN = (int) 1e5 + 5; int fact[MAXN + 1], invfact[MAXN + 1]; inline int comb(int n, int k) { if(n < k) return 0; return (1LL * fact[n] * (1LL * invfact[k] * invfact[n - k] % MOD)) % MOD; } int main() { //ifstream cin("A.in"); //ofstream cout("A.out"); int i, n, k; ios::sync_with_stdio(false); cin.tie(0), cout.tie(0); cin >> n >> k; fact[0] = invfact[0] = 1; for(i = 1; i <= n + 1; i++) { fact[i] = (1LL * fact[i - 1] * i) % MOD; invfact[i] = lgput(fact[i], MOD - 2); } k--; int ans = 0; for(i = 0; i <= k; i++) { int cur = (1LL * comb(n + 1, i) * lgput(k - i + 1, n)) % MOD; if(i & 1) { cur *= -1; } ans += cur; if(ans < 0) { ans += MOD; } if(ans >= MOD) { ans -= MOD; } } cout << ans; //cin.close(); //cout.close(); return 0; }
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