*/
Given an array nums of n integers where n > 1,
return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].

Example:

Input:  [1,2,3,4]
Output: [24,12,8,6]
Note: Please solve it without division and in O(n).
*/

class Solution {
    public int[] productExceptSelf(int[] nums) {
        if (nums.length < 2) {
            throw new IllegalArgumentException("Array must have more than 2 numbers to compute product");
        }
        int[] productsBeforeIndex = getProductsBeforeIndex(nums);
        int[] productsAfterIndex = reverseArray(getProductsBeforeIndex(reverseArray(nums)));

        return productsOfTwoArrays(productsBeforeIndex, productsAfterIndex);
    }

    public int[] getProductsBeforeIndex(int[] a) {
        int[] res = new int[a.length];
        res[0] = 1;
        for (int i = 1; i < a.length; i++) {
            res[i] = res[i - 1] * a[i - 1];
        }
        return res;
    }

    public int[] reverseArray(int[] a) {
        for (int i = 0; i < a.length / 2; i++) {
            int temp = a[i];
            a[i] = a[a.length - 1 - i];
            a[a.length - 1 - i] = temp;
        }
        return a;
    }

    public int[] productsOfTwoArrays(int[] a1, int[] a2) {
        int[] res = new int[a1.length];
        for (int i = 0; i < a1.length; i++) {
             res[i] = a1[i] * a2[i];
        }
        return res;
    }
}