解法一：贪心

两个数组分别按升序排列，然后正数和正数相乘、负数和负数相乘，且两者的绝对值尽可能大（数学原理）。

#include <bits/stdc++.h>
using namespace std;
long long A[100005], B[100005];
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int lenA, lenB;
    cin >> lenA;
    for (int i = 0; i < lenA; ++i) {
        cin >> A[i];
    }
    cin >> lenB;
    for (int i = 0; i < lenB; ++i) {
        cin >> B[i];
    }
    sort(A, A + lenA);
    sort(B, B + lenB);
    double total = 0;
    int head = 0, tail = lenB - 1;
    for (int i = 0; i < lenA; ++i) {
        if (A[i] < 0) {
            if (B[head] < 0) {
                total += A[i] * B[head];
                ++head;
            }
        } else {
            break;
        }
    }
    for (int i = lenA - 1; i >= 0; --i) {
        if (A[i] > 0) {
            if (B[tail] > 0) {
                total += A[i] * B[tail];
                --tail;
            }
        } else {
            break;
        }
    }
    cout << fixed;
    cout << setprecision(0) << total << '\n';
}