Pattern Recognition Drill
Easy Binary Search
The Problem
Given a sorted array and a target value, return the index of the target or -1 if not found.
What approach would you use?
Think about it before scrolling down.
lo=0, hi=n-1. Compare mid. If target < mid, search left; if target > mid, search right. O(log n).
Common Trap
Watch the off-by-one: lo <= hi (not lo < hi). And mid = lo + (hi-lo)//2 avoids overflow.