Question

I am tring to solve a Spoj problems of Binary Search but I keep getting “wrong answer” and I can’t see my problem.
Here is my bsearch function:

int binarySearch(int numbers[], int size, int key)
{
    int start = 0;
    int end = size - 1;
    int middle;

    while(start <= end)
    {
        middle = start + (end - start)/2;

        if(key < numbers[middle])
            end = middle - 1;
        else if(key > numbers[middle])
            start = middle + 1;
        else
            return middle;
    }

    return -1;
}

And this is my main function

int main()
{
    int *numbers;
    int n_numbers, n_queries, key, i, found;

    scanf("%d %d", &n_numbers, &n_queries);
    numbers = (int*)malloc(n_numbers * sizeof(int));

    for(i = 0; i<n_numbers; i++)
        scanf("%d", &numbers[i]);

    for(i = 0; i<n_queries; i++)
    {
        scanf("%d", &key);
        found = binarySearch(numbers, n_numbers, key);
        printf("%d\n", found);
    }

    return 0;
}

Here is the SPOJ problem:
http://www.spoj.com/problems/BSEARCH1/

Answer 1

The problem is that you are required to return the location of the first occurrence (starting from zero), and you are returning as soon as you find the key.

But it’s possible that the array is:
0 1 1 1 1 1 1 1 1 1 1 1 2

And the key is 1. You should return 1 (the location of the first occurence) and instead you are returning 6.