The binary search algorithm in the text makes recursive on subarrays of the array passed to the algorithm. The range passed to the search function is first to last. The search algorithm makes recursive calls on the left or right subarray that target will be in, if the target is present. What are the left and right ends of the left subarray?

Question

a) first, mid – 1
b) first, mid + 1
c) mid – 1, left
d) mid + 1, left
e) left, mid

Answer 1

a) first, mid – 1

The middle element has been eliminated by the following code fragment that occurs before the recursive calls:
```
if(key == a[mid])
{
found = true; location = mid;
}
```
The range will start with index first and run to index one before mid, namely, mid - 1. The rest of the answers have off-by-one errors, or they get the range backwards, or both.