Searching Algorithms: Binary and Linear Search

Binary search is the algorithm most engineers believe they know and most implement incorrectly under pressure. The idea takes a sentence; the boundary conditions are where interviews are actually lost.

Stepping through the search space narrowing makes the invariant visible, which is what makes the boundary decisions derivable rather than memorised. That matters because binary search rarely appears in interviews as "search this sorted array" — it appears disguised, applied to an answer space rather than an input array, and recognising it depends on understanding the invariant rather than the template.