【算法題】最大乘積

給定一個無序數組，包含正數、負數和0，要求從中找出3個數的乘積，使得乘積最大，要求時間複雜度：O(n)，空間複雜度：O(1)

輸入描述:
無序整數數組A[n]

輸出描述:
滿足條件的最大乘積

輸入例子1:
4
3 4 1 2

輸出例子1:
24

---

#include <iostream>
#include <string>
#include <cstring>
#include <vector>
#include <numeric>
#include <algorithm>
using namespace std;
//#define debug_

vector<long long> A;

long long func()
{
    vector<long long > Positive(3,0);
    vector<long long> Negative(3,0);
    for (auto i = 0; i < A.size();++i)
    {
        if (A[i] > 0)
        {
            Positive[2] = max(Positive[1] * A[i], Positive[2]);
            Negative[2] = min(Negative[1] * A[i], Negative[2]);
        }
        else
        {
            Positive[2] = max(Negative[1] * A[i], Positive[2]);
            Negative[2] = min(Positive[1] * A[i], Negative[2]);
        }
        if (A[i] > 0)
        {
            Positive[1] = max(Positive[0] * A[i], Positive[1]);
            Negative[1] = min(Negative[0] * A[i], Negative[1]);
        }
        else
        {
            Positive[1] = max(Negative[0] * A[i], Positive[1]);
            Negative[1] = min(Positive[0] * A[i], Negative[1]);
        }
        Positive[0] = max(A[i], Positive[0]);
        Negative[0] = min(A[i], Negative[0]);

    }
    return Positive[2];

}

int main()
{
    int n;
    cin >> n;
    int tmp(0);
    A.resize(n);
    for (auto i = 0; i < n;++i)
    {
        cin >> A[i];
    }
    cout << func() << endl;
    return 0;
}

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