# Java O(n) solution, no extra space with explanation

• Because we cannot use division, so assume we have two integer arrays with the same length of nums, `int[] leftProd = new int[nums.length]; int[] rightProd = new int[nums.length]`, we store the product of all the left elements in `leftProd` and the product of all the right elements in `rightProd`, then the product of `leftProd[i]` and `rightProd[i]` will be the value we want to put into the result.

Take the example of `num[] = {2, 4, 3, 6}`, then `leftProd` will be `{1, 2, 8, 24}` , and rightProd will be `{72, 18, 6, 1}`.

``````public class Solution {
public int[] productExceptSelf(int[] nums) {
if(nums == null)
return null;
int[] res = new int[nums.length];
for(int i = 0; i < nums.length; i++){
if(i == 0)
res[i] = 1;
else
res[i] = res[i - 1] * nums[i - 1];
}
int prod = 1;
for(int i = nums.length - 1; i >= 0; i--){
res[i] = res[i] * prod;
prod *= nums[i];
}
return res;
}
``````

}

• This post is deleted!

• "no extra space"? I see `i` and `prod`.

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