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

package arrays;

/* * Given a sorted array, find the number of times an element occured. * Binary search O(lgn) * */

public class NumberOfN {

static int bSearchLeft(int[] arr, int start, int end, int n){

    while(start < end){

        int mid = (start + end)>>1;
        if(arr[mid] < n){
            start = mid + 1;
        }else{
            end = mid;
        }

    }

    return end;
}

static int bSearchRight(int[] arr, int start, int end, int n){

    while(start < end){

        int mid = (start + end)>>1;
        if(arr[mid] <= n){
            start = mid + 1;
        }else{
            end = mid;
        }

    }

    return end;
}

/**
 * @param args
 */
public static void main(String[] args) {

    int[] arr = new int[]{3,3,3,3};
    int n = 3;
    int indexLeft = bSearchLeft(arr, 0, arr.length, n);
    int indexRight = bSearchRight(arr, 0, arr.length, n);
    System.out.println(indexLeft + " " +indexRight);
    System.out.println("Number of occurences: " + (indexRight - indexLeft));
}

}