diff options
Diffstat (limited to 'content/math/transforms/ntt.cpp')
| -rw-r--r-- | content/math/transforms/ntt.cpp | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/content/math/transforms/ntt.cpp b/content/math/transforms/ntt.cpp new file mode 100644 index 0000000..ca605d3 --- /dev/null +++ b/content/math/transforms/ntt.cpp @@ -0,0 +1,23 @@ +constexpr ll mod = 998244353, root = 3; + +void ntt(vector<ll>& a, bool inv = false) { + int n = sz(a); + auto b = a; + ll r = inv ? powMod(root, mod - 2, mod) : root; + + for (int s = n / 2; s > 0; s /= 2) { + ll ws = powMod(r, (mod - 1) / (n / s), mod), w = 1; + for (int j = 0; j < n / 2; j += s) { + for (int k = j; k < j + s; k++) { + ll u = a[j + k], t = a[j + s + k] * w % mod; + b[k] = (u + t) % mod; + b[n/2 + k] = (u - t + mod) % mod; + } + w = w * ws % mod; + } + swap(a, b); + } + if (inv) { + ll div = powMod(n, mod - 2, mod); + for (auto& x : a) x = x * div % mod; +}} |