152. Product maximum subarray

subject

Give you an array of integers nums , Please find the non empty continuous subarray with the largest product in the array （ The subarray contains at least one number ）, And returns the product of the subarray .
The answer to the test case is 32- position Integers . Subarray Is a continuous subsequence of an array .
Example ：

！！！ Be careful

For multiplication , We need to pay attention , Negative number multiplied by negative number , Will become a positive number , So when solving this problem, we need Maintain two variables , Current maximum , And the minimum , The minimum value may be negative , But maybe the next step is to multiply by a negative number , The current maximum becomes the minimum , And the minimum becomes the maximum .

Code

class Solution {
    
    public int maxProduct(int[] nums) {
    
        int len = nums.length;
        int[] maxNum = new int[len];
        int[] minNum = new int[len];
        int ans = nums[0];
        // initialization 
        maxNum[0] = nums[0];
        minNum[0] = nums[0];
        for(int i = 1; i < len; i++){
    
            maxNum[i] = Math.max(nums[i],Math.max(maxNum[i-1]* nums[i] , minNum[i-1] * nums[i]));
            minNum[i] = Math.min(nums[i],Math.min(minNum[i-1]*nums[i],maxNum[i-1] * nums[i]));
            ans = Math.max(ans,maxNum[i]);
        }
        return ans;
    }
}