Function inv

code/mathematics/ntt.cpp:35–43

    Num ni = Num(n).inv();
    rep(i,0,n) { x[i] = x[i] * ni; } } }
void inv(Num x[], Num y[], int l) {
  if (l == 1) { y[0] = x[0].inv(); return; }
  inv(x, y, l>>1);
  // NOTE: maybe l<<2 instead of l<<1
  rep(i,l>>1,l<<1) T1[i] = y[i] = 0;
  rep(i,0,l) T1[i] = x[i];
  ntt(T1, l<<1); ntt(y, l<<1);
  rep(i,0,l<<1) y[i] = y[i]*2 - T1[i] * y[i] * y[i];
  ntt(y, l<<1, true); }
void sqrt(Num x[], Num y[], int l) {
  if (l == 1) { assert(x[0].x == 1); y[0] = 1; return; }
  sqrt(x, y, l>>1);