Summary

Binary search is a fast way to locate an item in a sorted list by repeatedly checking the middle element and discarding the half that can’t contain the answer.

• Requirement: the data must be sorted (commonly ascending).
• Idea: compare the middle value to the target, then keep only the left or right half.
• Result: returns the matching index (or “not found” if the target isn’t present).

Performance: O(log n) time, O(1) extra space.