给定一个无序数组,包含正数、负数和0,要求从中找出3个数的乘积,使得乘积最大,要求时间复杂度:O(n),空间复杂度:O(1)
输入描述:
无序整数数组A[n]
输出描述:
满足条件的最大乘积
输入例子1:
4
3 4 1 2
输出例子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;
}