152_maxProduct.java

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

//Follow up: no need dp array to save, just need save preMin, preMax, to calculate min, max, then make it as previous
public class Solution {
    public int maxProduct(int[] nums) {
        int res = nums[0];
        int preMin = nums[0];
        int preMax = nums[0];
        int min = 0;
        int max = 0;
        for(int i = 1; i < nums.length; i++){
            min = Math.min(Math.min(nums[i], nums[i]*preMin),nums[i]*preMax);
            max = Math.max(Math.max(nums[i], nums[i]*preMin),nums[i]*preMax);
            res = Math.max(res, max);
            preMin = min;
            preMax = max;
        }
        return res;
    }
}