Remove duplicate in-place from sorted array

1. Use Set
   1. Insert in Set: NLog(N) + Time O(N)
   2. Space O(N)
2. 2 Pointer

   1.  	fun(){
       	int fP = 0;
       	int sP = 1;
       		for(int sP=1, sP<n;sP++){
       			if(a[fP] != a[sP])
       			{
       				a[fP+1] = a[sP];
       				fP++;
       			}	
       		}
       		return fP+1;
       	}

Time: O(N)
Space: O(1)