BZOJ2194 Fast Fourier II

And then the title exposes everything.

Read B upside down and it becomes convolution (what is that ...?). can you eat it? ) in the form

So it's just a little bit of an FFT.

1 /**************************************************************2 problem:21943 User:rausen4 language:c++5 result:accepted6 time:2760 Ms7 memory:21900 KB8 ****************************************************************/9  Ten#include <cstdio> One#include <cmath> A#include <algorithm> -   - #defineComplex P the using namespacestd; -typedefDoubleLF; - Const intN =300005; - ConstLF pi = ACOs (-1); +   - structComplex { + lf x, y; A P () {} at P (LF _x, LF _y): X (_x), Y (_y) {} -       -Inline Poperator+ (ConstP &x)Const { -         returnP (x + x.x, y +x.y); -     } -Inline Poperator- (ConstP &x)Const { in         returnP (x-x.x, Y-x.y); -     } toInline Poperator* (ConstP &x)Const { +         returnP (x * x.x-y * x.y, X * x.y + y *x.x); -     } the       *Inlinevoid operator+= (ConstP &X) { $* This= * This+X;Panax Notoginseng     } -Inlinevoid operator*= (ConstP &X) { the* This= * This*X; +     } A} X[n], y[n], w[2][n]; the   + intN, Len; - intA[n], b[n]; $   $InlineintRead () { -     intx =0; -     CharCH =GetChar (); the      while(Ch <'0'||'9'<ch) -CH =GetChar ();Wuyi      while('0'<= CH && Ch <='9') { thex = x *Ten+ CH-'0'; -CH =GetChar (); Wu     } -     returnx; About } $   - voidFFT (P *x,intLenintv) { -     intI, J, L; - P tmp; A      for(i = j =0; i < Len; ++i) { +         if(I >j) Swap (X[i], x[j]); the          for(L = Len >>1; (J ^= L) < L; L >>=1); -     } $      for(i =2; I <= Len; I <<=1) the          for(j =0; J < Len; J + =i) the              for(L =0; L < i >>1; ++l) { theTMP = x[j + L + (i >>1)] * w[v][len/i *l]; theX[j + L + (i >>1)] = X[j + L]-tmp; -X[j + L] + =tmp; in             } the } the   About voidWork () { the     inti; the      for(len =1; Len < n <<1; Len <<=1); the      for(i =0; I <= Len; ++i) +w[1][len-i] = w[0][i] = P (cos (pi *2* I/len), sin (pi *2Ilen)); -           the      for(i =0; i < Len; ++i)BayiX[i] = P (A[i],0), y[i] = P (B[i],0); theFFT (x, Len,0), FFT (Y, Len,0); the       -      for(i =0; i < Len; ++i) -X[i] *=Y[i]; theFFT (x, Len,1); the   the      for(i = n-1; i +1< n <<1; ++i) theprintf"%d\n", (int) Round (x[i].x/len)); - } the   the intMain () { the     inti;94n =read (); the      for(i =0; I < n; ++i) theA[i] = Read (), B[n-i-1] =read (); the Work ();98     return 0; About}

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(P.S xs I'm back!!! ）

BZOJ2194 Fast Fourier II