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

Solve it without division and in O(n).

For example, given [1,2,3,4], return [24,12,8,6].

Follow up:
Could you solve it with constant space complexity? (Note: The output array does not count as extra space for the purpose of space complexity analysis.)

解答：
来自discussion里的解：

public int[] productExceptSelf(int[] nums) {
    int[] result = new int[nums.length];
    //left side product
    result[0] = 1;
    for (int i = 1; i < nums.length; i++) {
        result[i] = result[i - 1] * nums[i - 1];
    }
    //right side product
    int right = 1;
    for (int i = nums.length - 1; i >= 0; i--) {
        result[i] *= right;
        right *= nums[i];
    }
    
    return result;
}