Efficient way to count occurrences of a key in a sorted array

Question

This was asked in on-site Microsoft interview.

Count the number of occurrences of a given key in an array.

I answered linear search because the elements may be s

Answer 1

You can use recursive version of binary search

int modifiedbinsearch_low(int* arr, int low, int high , int key)
{   
    if(low==high) return high ; 

    int mid = low + (high-low) /2;

    if(key >  arr[mid] ) { modifiedbinsearch_low(arr,mid + 1 , high,key);  } 
    else  { modifiedbinsearch_low(arr,low,mid,key);  }  
}
int modifiedbinsearch_high(int* arr, int low, int high , int key)
{   
    if(low==high) return high ; 

    int mid = low + (high-low) /2;

    if(key <  arr[mid] ) { modifiedbinsearch_high(arr,low,mid,key);  } 
    else  { modifiedbinsearch_high(arr,mid+1,high,key);  } 

} 

.

int low = modifiedbinsearch_low( ...)

int high = modifiedbinsearch_high( ...)

(high - low) gives the number of keys