DE-Shaw interview question

what is wrong with my code given below ANY HELP WILL BE APPRECIATED
my code:

struct ${
int start,end;
};

bool cmp( a, b){
return (a.end<b.end);
}

class Solution{
public:
int findPlatform(int arr[], int dep[], int n)
{
$ a[n];
for(int i=0;i<n;i++) a[i].start=arr[i],a[i].end=dep[i];
sort(a,a+n,cmp);

	int max_count=0,count=1;
	$ flag=a[0];
	for(int i=1;i<n;i++)
	{
	  if(flag.end>=a[i].start) count++;
	  else 
	  {
	      flag=a[i];
	      max_count=max(max_count,count);
	      count=1;
	  }
	}
    return max_count;
}

};