乘积最大子数组

维护两个dp数组来处理负值问题

class Solution {
 public:
  int maxProduct(vector<int>& nums) {
    int n = nums.size();
    vector<int> maxF(n), minF(n);
    maxF[0] = minF[0] = nums[0];
    for (int i = 1; i < nums.size(); ++i) {
      maxF[i] = max(maxF[i - 1] * nums[i], max(nums[i], minF[i - 1] * nums[i]));
      minF[i] = min(minF[i - 1] * nums[i], min(nums[i], maxF[i - 1] * nums[i]));
    }
    return *max_element(maxF.begin(), maxF.end());
  }
};