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MEDIUMArray, Binary Search, Sliding Window, Prefix SumThis problem sounds like a bit-flipping question, but the useful reframe is simpler:
find the longest contiguous subarray that contains at most k zeroes.
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MEDIUMArray, Dynamic ProgrammingThis problem asks for the contiguous subarray whose product is as large as possible.
That sounds close to Maximum Subarray, but products behave very differently from sums. With sums, a very negative running total is usually bad news. With products, a very negative running product can suddenly become the best thing to keep if the next number is also negative.
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MEDIUMArray, Dynamic Programming, MatrixThe input is a grid of "0" and "1" values. The job is to find the area of the largest square made entirely of 1s.
The part that usually traps people is the word “square.” A brute-force approach tends to ask:
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MEDIUMArray, Breadth-First Search, MatrixThe grid has three kinds of cells: empty (0), fresh oranges (1), and rotten oranges (2). Every minute, any fresh orange touching a rotten orange in the four main directions also becomes rotten.
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HARDArray, Binary Search, Dynamic Programming, Greedy, Prefix SumThe input array must be cut into exactly k non-empty, contiguous pieces. Each cut creates one subarray, and the score of a split is the largest subarray sum that appears anywhere in that split.
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MEDIUMArray, Binary SearchThe array is sorted, and every value appears exactly twice except for one value that appears once.
If the array were not sorted, the quickest idea would be XOR: identical values
cancel out, so the final XOR is the answer. That works in O(n) time and
O(1) space.
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Difficulty: MEDIUM
Problem: Sort an Array
The task is deliberately simple to state: given an integer array, return the same values in ascending order. The interview signal is not whether someone knows Python’s built-in sort, but whether they can implement a sorting strategy with clear time and space guarantees.
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HARDArray, Dynamic Programming, Stack, Matrix, Monotonic StackThe matrix contains only "0" and "1", and the goal is to find the area of
the largest axis-aligned rectangle made entirely of "1" cells.
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MEDIUMArray, Math, Two PointersThe problem gives an array nums and an integer k. The task is to rotate the
array to the right by k positions, modifying the original list in place.
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MEDIUMDepth-First Search, Breadth-First Search, Graph Theory, Topological SortThere are numCourses courses labeled from 0 to numCourses - 1.
Each prerequisite pair [a, b] means course b must be finished before course a.