D. Zero Quantity Maximization（hash+map）

#include<iostream>
#include<map>
using namespace std;

#define ll long double

map<ll, int>ss;
const long long mod = 1e17 + 7;
const int maxn = 2e5+10;


int a[maxn], b[maxn];
int n, maxx;


int gcd(int a, int b){ return b == 0 ? a : gcd(b, a%b); }
int ans;
int main(){
    cin >> n;
    for (int i = 1; i <= n; ++i)
    {
        cin >> a[i];
    }
    for (int i = 1; i <= n; ++i)
        cin >> b[i];

    for (int i = 1; i <= n; ++i){
        if (a[i] == 0){ ans += (b[i] == 0); continue; }
        int d = gcd(a[i], b[i]);
        a[i] /= d;  b[i] /= d;
        ss[a[i] * 1.0 / b[i]]++;
    }


    for (map<ll, int>::iterator it = ss.begin(); it != ss.end(); ++it){
        if (it->second > maxx)maxx = it->second;
    }
    cout << maxx+ans << endl;
}