loj#6487 基础 FFT 练习题

分析

仔细观察a[i],b[i]的数据范围

于是我们转为枚举所有a[i],b[i]的值

然后暴力即可

代码

#include<bits/stdc++.h>
using namespace std;
#define abs(x) x>0?x:-x
int s[1000100],sum1[1000100],sum2[1000100],a[1000100],b[1000100],n,c1,c2;
long long Ans;
inline int ra(){
    int x=0;char s=getchar();
    while(!isdigit(s))s=getchar();
    while(isdigit(s))x=(x<<3)+(x<<1)+(s-'0'),s=getchar();
    return x;
}
int main(){
    int t,i,j,k;
    for(i=1;i<=1000;++i)s[i*i]=i;
    for(i=2;i<=1000000;++i)s[i]=(s[i]?s[i]:s[i-1]);
    t=ra();
    while(t--){
      n=ra();
      for(i=1;i<=n;++i){
          k=ra();
          sum1[k]?:a[++c1]=k;
          sum1[k]++;
      }
      for(i=1;i<=n;++i){
          k=ra();
          sum2[k]?:b[++c2]=k;
          sum2[k]++;
      }
      for(i=1;i<=c1;++i){
          for(j=1;j<=c2;++j)
            Ans+=1ll*sum1[a[i]]*sum2[b[j]]*s[abs((a[i]-b[j]))];
          sum1[a[i]]=0;
      }
      for(i=1;i<=c2;++i)sum2[b[i]]=0;
      cout<<Ans<<"\n";
      c1=c2=Ans=0;
    }
    return 0;
}