space complexity of recursive function

Hi,

this function has to check if an array is not descending it has to be recursive and it's space complexity has to be O(log(n))

Code:

---

int is_sorted(int a[ ], int n)
{
 int check=n-1;
 if(n==1 || n==0) return 1;
if(a[check]<a[check-1])return 0;
 else return(is_sorted(a,n-1));
}


---

this is what i came up with. i know it's space complexity is O(n) how do i make it O(log(n))?

Also here -> Space complexity of recursive function - Dev Shed

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The guy who said this got it right:
"An O(log(n)) space complexity algorithm divides intervals in half."

Consider the first, middle and last items, then perform two recursive calls. That's all I'm prepared to say.