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feat(number/factorial): add combinatoric function without MLL

This commit is contained in:
arielherself 2025-01-07 16:42:48 +08:00
parent b33b8ed3f4
commit dfd419ac95
Signed by: arielherself
SSH Key Fingerprint: SHA256:AK3cyo9tFsp7Mox7K0sYphleC8hReXhnRKxwuDT5LBc
1 changed files with 12 additions and 5 deletions
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17
number/examples/factorial-inverse-in-linear.cc
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@ -1,20 +1,27 @@
constexpr int M = MDL;
constexpr int N = 3e6 + 10; constexpr int N = 3e6 + 10;
ll fact[N], factrev[N + 1], s[N + 1]; ll fact[N], factrev[N + 1], s[N + 1];
void prep() { void prep() {
fact[0] = factrev[0] = 1; fact[0] = factrev[0] = 1;
for (int i = 1; i < N; ++i) { for (int i = 1; i < N; ++i) {
fact[i] = (fact[i - 1] * i) % MDL; fact[i] = (fact[i - 1] * i) % M;
} }
s[0] = 1; s[0] = 1;
for (int i = 1; i <= N; ++i) { for (int i = 1; i <= N; ++i) {
s[i] = s[i - 1] * fact[i - 1] % MDL; s[i] = s[i - 1] * fact[i - 1] % M;
} }
factrev[N] = inverse(s[N], MDL); factrev[N] = inverse(s[N], M);
for (int i = N; i; --i) { for (int i = N; i; --i) {
factrev[i - 1] = factrev[i] * fact[i - 1] % MDL; factrev[i - 1] = factrev[i] * fact[i - 1] % M;
} }
for (int i = 0; i < N; ++i) { for (int i = 0; i < N; ++i) {
factrev[i] = factrev[i + 1] * s[i] % MDL; factrev[i] = factrev[i + 1] * s[i] % M;
} }
} }
ll mycomb(int n, int k) {
if (n < 0 or k < 0 or n < k) return 0;
return fact[n] * factrev[k] % M * factrev[n - k] % M;
}