Question

I’ve found the following code online,

int binary_search(int a[], int low, int high, int target) {
    if (high < low)
        return -1;
    int middle = (low + high)/2;
    if (target < a[middle])
        return binary_search(a, low, middle-1, target);
    else if (target > a[middle])
        return binary_search(a, middle+1, high, target);
    else if (target == a[middle])
        return middle;
}

My function has a specified prototype(meaning that it has a set number of arguments that cannot be altered) this is what I have so far

bool search(int value, int array[], int n) {
    if (array[n/2] == value)
        return 1; 
    else if (array[n/2] < value)
        return search(value, &array[n/2], (n)/2);
    else
        // how do I "return" the other half?
}

Does my implementation look correct so far? I can’t seem to figure out how to implement the final else statement.

Answer 1

high and low represent the bounds of subarray in which continue the research. If you analyze the code you’ll notice that if target is smaller that a[middle] you’ll have to continue the research in the first half of the array (in fact it calls binary_search passing the same low bound but, as a superior bound, the actual middle-1). On the other side, if target is greater that a[middle] you’ll have to continue the research in the second half of the array (from middle+1 to high). Of course, if target is equal to a[middle] you’ve finished.