intermediate
10 min read
Find First and Last Position of Element in Sorted Array
A standard binary search finds a match. This problem asks for the entire matching block. The difference is one boundary decision.
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Modified Binary Search
Use binary search for ordered lookup, boundaries, rotated arrays, peaks, and monotonic partitions.
Problems
Problems in Modified Binary Search
Practice problems that share this primary solution pattern and compare the clues that reveal it.
intermediate
12 min read
Search in Rotated Sorted Array
Rotation breaks global order, not all order. Find the sorted half, test its value range, and discard what that range proves impossible.
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beginner
10 min read
Search Insert Position
This problem asks for more. If the target is absent, return the index where it could be inserted while keeping the array sorted.
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expert
14 min read
Median of Two Sorted Arrays
Merging is the obvious solution. It is also disqualified by the runtime requirement. The useful reframe is to search for a cut, not for a value: place…
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intermediate
10 min read
Search a 2D Matrix
A matrix can be two-dimensional storage with a one-dimensional search space. Prove that shape first, then run ordinary binary search over virtual indices.
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intermediate
11 min read
Search in Rotated Sorted Array II
Duplicates turn a clean binary-search decision into an information problem. When nums[left], nums[mid], and nums[right] are equal, you cannot tell which…
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