Generated by Codex with GPT-5
MEDIUMArray, Two Pointers, SortingThe input array contains only 0, 1, and 2. Those values represent three categories, and the goal is to reorder the array in place so all 0s come first, then all 1s, then all 2s.
Generated by Codex with GPT-5
HARDArray, BacktrackingThe board details can make this problem look more complicated than it is.
At a higher level, the task is:
That “one queen per row” reframing is the key simplification.
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MEDIUMArray, Dynamic ProgrammingEach house has some amount of money. The thief wants the largest total possible, but robbing two neighboring houses triggers the alarm.
So the real question is:
At every house, is it better to:
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MEDIUMString, Dynamic Programming, BacktrackingGiven n pairs of parentheses, generate every string that is:
2n characters long( and )The last condition is the important one.
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MEDIUMArray, Binary SearchThe array started out sorted in ascending order, then got rotated at some pivot.
That means a sequence like [0, 1, 2, 4, 5, 6, 7] might become [4, 5, 6, 7, 0, 1, 2].
Generated by Codex with GPT-5
MEDIUMArray, Binary SearchThe input array is sorted, and the target value may appear many times in one contiguous block.
The task is not just to decide whether the target exists. It is to return the exact starting and ending indices of that block.
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MEDIUMArray, Hash Table, String, SortingTwo strings belong in the same group if they use the exact same letters with the exact same counts, just in a different order.
So the problem is not really about comparing every string against every other string. It is about finding a stable “signature” for each word, so all words with the same signature land in the same bucket.
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MEDIUMArray, Matrix, SimulationThe input is a 2D matrix. The task is to return every value exactly once in spiral order:
This is a traversal problem. Nothing in the matrix needs to be modified. The only challenge is knowing when to turn and when a side has already been fully consumed.
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MEDIUMArray, Dynamic Programming, GreedyEach position tells how far the player is allowed to jump from that spot.
The goal is not to find the minimum number of jumps. It is only to decide whether the last index is reachable at all.
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MEDIUMArray, Hash Table, Union-FindThe input is an unsorted integer array. The task is to find the length of the longest run of values that can be arranged as x, x + 1, x + 2, ....