152. The product of the maximum Leetcode title sequences (dynamic programming - Medium)

Subject description:

Given an array of integers  nums , to find a product of the maximum sequence of contiguous subsequence (which comprises at least a sequence number).

Example 1:

Input: [2,3, 2,4]
Output: 6
Explanation: subarray [2,3] maximum product 6.
Example 2:

Input: [-2,0, -1]
Output: 0
Explanation: The results can not be 2, since the [-2, -1] is not subarray.

Analysis of ideas:

Tags: dynamic programming
to calculate a current maximum value to iterate, constantly updated
current imax is the maximum order, the current maximum value imax = max (imax * nums [ i], nums [i])
due to the presence of negative, it will result in maximum becomes the smallest, smallest becomes the largest. It is also necessary to maintain this minimum value imin, imin = min (imin * nums [i], nums [i])
When the negative appears imax and imin exchange before proceeding calculation
time complexity: O (n)

class Solution {
    public int maxProduct(int[] nums) {
        int max = Integer.MIN_VALUE, imax = 1, imin = 1;
        for(int i=0; i<nums.length; i++){
            if(nums[i] < 0){ 
              int tmp = imax;
              imax = imin;
              imin = tmp;
            }
            imax = Math.max(imax*nums[i], nums[i]);
            imin = Math.min(imin*nums[i], nums[i]);
            
            max = Math.max(max, imax);
        }
        return max;
    }
}