zyBooks_17_algs_1
You are given an alphabetically sorted list of strings read from input. The goal is to complete the find() function, which passes the following test cases ( included in the screen shot)

range_size: The total number of elements between low_index and high_index (both inclusive).
middle_index: The index calculated by floor division (//) of the sum of low_index and high_index.
The element at middle_index in the list.

Complete the following code by choosing the correct option for the missing lines of code. Which of the following is the correct code to complete the find() function?

Question

zyBooks_17_algs_1
You are given an alphabetically sorted list of strings read from input. The goal is to complete the find() function, which passes  the following test cases ( included in the screen shot)

range_size: The total number of elements between low_index and high_index (both inclusive).
middle_index: The index calculated by floor division (//) of the sum of low_index and high_index.
The element at middle_index in the list.

Complete the following code by choosing the correct option for the missing lines of code. Which of the following is the correct code to complete the find() function?

BlackTom AI · Accepted Answer

We start by restating the problem in our own terms: we have a sorted list of strings and need to complete the find() function. The inputs relevant to the missing lines are low_index and high_index, representing a inclusive range within the list. We must compute two quantities: range_size, the total number of elements from low_index to high_index inclusive, and middle_index, the index of the middle element within that range, using floor division.
Option A: "range_size = len(all_names) - 1middle_index = high_index // 2"
- This choice uses the total length of the list (len(all_names)) and subtracts 1, which does not reflect the size of the current search range and would be incorrect for arbitrary low_index and high_index. The middle_index calculation uses high_index // 2, which ignores low_index and does not locate the middle of the current range. Taken together, this option does not compute the intended range size or a correct middle index for a subrange.
Option B: "range_size = (high_index - low_index) + 1middle_index = (low_index + high_index) // 2"
- This option correctly expresses the number of elements in an inclusive range: high_index minus low_index plus 1. The middle_index is computed as the floor of the average of low_index and high_index, which yields the central position within the inclusive range. This aligns with standard binary search logic where you repeatedly select the middle element of the current range.
Option C: "range_size = len(all_names)middle_index = (low_index + high_index) / 2"
- Here, range_size uses the full list length, not the current subrange, which is inappropriate for a binary search over a subset. Additionally, the middle_index uses a division by 2 (/) instead of floor division (//). In many languages this would produce a floating-point value, which cannot serve as an array index and would require rounding. Both parts are incorrect for the intended algorithm.
Option D: "range_size = high_index - low_indexmiddle_index = (low_index + high_index) % 2"
- This option omits the inclusive +1 in the range size, yielding one less than the actual count for inclusive indices. The middle_index calculation uses modulo 2, which yields 0 or 1, not a valid index within the current range except in a very limited sense; it does not locate the actual middle element. Therefore, this option miscomputes both required quantities.

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