Binary Search
Given a sorted array nums and an integer target Return the index of target if it exists, otherwise return -1 Must use O(log n) time complexity Example: nums = [-1,0,3,5,9,12], target = 9 => 4
Find a target in a sorted array. It's the most fundamental divide-and-conquer algorithm, and getting the boundary conditions exactly right is trickier than it looks. Interviewers use it as a baseline—if you fumble binary search, they'll wonder about everything else.
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