238. Product of Array Except Self

Approach

i	0	1	2	3
nums	1	2	3	4
leftProduct	1	1	2	6
rightProduct	24	12	4	1
ans	24	12	8	6

Product expect self is product of leftProduct and rightProduct. Instead of computing leftProduct and rightProduct and then computing ans. Compute leftProduct and while computing rightProduct, computer ans too.

Code

public int[] productExceptSelf(int[] nums) {
  int res[] = new int[nums.length];

  int leftProduct = 1;
  for (int i = 0; i < nums.length; i++) {
    res[i] = leftProduct;
    leftProduct *= nums[i];
  }

  int rightProduct = 1;
  for (int i = nums.length - 1; i >= 0; i--) {
    res[i] *= rightProduct;
    rightProduct *= nums[i];
  }

  return res;
}