What happens if binary search is used on an unsorted list?

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BlackTom AI · Accepted Answer

Consider the problem: what happens if binary search is used on an unsorted list?
Option 1: 'It will convert the list to a tree' - This is incorrect. Using binary search does not transform the data structure into a tree; binary search relies on a sorted order to halve the search space, not on restructuring the data.
Option 2: 'It will find the target but slower' - Binary search is efficient specifically because the list is sorted. If the list is unsorted, the algorithm cannot guarantee locating the target in fewer steps, and claiming it will find it slower is misleading without clarifying that correctness itself is not guaranteed; the fundamental issue is correctness, not merely speed.
Option 3: 'It will always find the target' - This is false. On an unsorted list, binary search can miss the target entirely because the decision to discard half the list is based on an order assumption that does not hold.
Option 4: 'It will raise a runtime error' - There is no intrinsic runtime error caused simply by applying binary search to an unsorted list; the algorithm’s behavior is undefined with respect to correctness, but not necessarily an exception.
Option 5: 'It will sort the list first' - Binary search does not automatically sort data; sorting is a separate operation. If you sort first, you could then apply binary search, but the statement describes an automatic behavior that is not how binary search operates.
Option 6: 'It may give incorrect results' - This is accurate. When the list is not sorted, the core invariant that guides binary search—namely, that the target lies in a specific half based on comparison results—does not hold, leading to possible incorrect conclusions or missed targets.
In summary, the key misconception is assuming that binary search can function correctly on unsorted data. The unsorted order breaks the divide-and-conquer logic, so the algorithm may fail to find the target or return an incorrect result, depending on the data and the implementation.

IS 4485-001 Fall 2025 Final Exam

What happens if binary search is used on an unsorted list?

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