Submission #1778175

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Source Code Expand

#include<bits/stdc++.h>

using namespace std;

namespace FastFourierTransform
{
  using C = complex< double >;

  void DiscreteFourierTransform(vector< C > &F, bool rev)
  {
    const int N = (int) F.size();
    const double PI = (rev ? -1 : 1) * acos(-1);
    for(int i = 0, j = 1; j + 1 < N; j++) {
      for(int k = N >> 1; k > (i ^= k); k >>= 1);
      if(i > j) swap(F[i], F[j]);
    }

    C wr, w, s, t;
    for(int i = 1; i < N; i <<= 1) {
      wr = polar(1.0, PI / i);
      for(int j = 0; j < N; j += i * 2) {
        w = 1.0;
        for(int k = 0; k < i; k++) {
          s = F[j + k], t = F[j + k + i] * w;
          F[j + k] = s + t, F[j + k + i] = s - t;
          w *= wr;
        }
      }
    }
    if(rev) {
      double temp = 1.0 / N;
      for(int i = 0; i < N; i++) F[i] *= temp;
    }
  }

  vector< int > Multiply(const vector< int > &A, const vector< int > &B)
  {
    int sz = 1;
    while(sz < A.size() + B.size() - 1) sz <<= 1;
    vector< C > F(sz), G(sz);
    for(int i = 0; i < A.size(); i++) F[i] = A[i];
    for(int i = 0; i < B.size(); i++) G[i] = B[i];
    DiscreteFourierTransform(F, false);
    DiscreteFourierTransform(G, false);
    for(int i = 0; i < sz; i++) F[i] *= G[i];
    DiscreteFourierTransform(F, true);
    vector< int > X(A.size() + B.size() - 1);
    for(int i = 0; i < A.size() + B.size() - 1; i++) X[i] = round(F[i].real());
    return (X);
  }
};


int main()
{
  int N;
  scanf("%d", &N);
  vector< int > A(N + 1), B(N + 1);
  for(int i = 0; i < N; i++) scanf("%d %d", &A[i + 1], &B[i + 1]);
  auto C = FastFourierTransform::Multiply(A, B);
  for(int i = 1; i <= 2 * N; i++) printf("%d\n", C[i]);
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:57:18: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &N);
                  ^
./Main.cpp:59:66: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
   for(int i = 0; i < N; i++) scanf("%d %d", &A[i + 1], &B[i + 1]);
                                                                  ^

Judge Result