Generated by Codex with GPT-5
MEDIUMArray, Two Pointers, SortingThe input is an integer array, and the goal is to return every unique triplet whose values add up to 0.
Two details make the problem harder than it looks:
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MEDIUMArray, Two PointersThe array represents one permutation of the numbers.
The task is to mutate it into the very next permutation in lexicographic order, which means:
If the current permutation is already the largest possible one, such as [3, 2, 1], then there is no larger answer. In that case, the correct result is the smallest permutation, which is ascending order.
Generated by Codex with GPT-5
MEDIUMString, Stack, RecursionThe input is an encoded string where patterns like 3[ab] mean “repeat ab three times.” The tricky part is that the repeated part can itself contain more encoded pieces, such as 3[a2[c]].
Generated by Codex with GPT-5
MEDIUMArray, Divide and Conquer, Dynamic ProgrammingThe input is an integer array, and the task is to choose one contiguous subarray whose sum is as large as possible.
The important constraint is contiguity. This is not “pick the best numbers anywhere in the array.” Once a starting point is chosen, the subarray must be one uninterrupted block.
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MEDIUMArray, SortingThe input is a list of inclusive intervals like [start, end]. The goal is to combine every set of overlapping intervals and return the smallest list of non-overlapping intervals that covers the same ranges.
Generated by Codex with GPT-5
MEDIUMMathGiven a signed 32-bit integer, reverse its decimal digits.
Examples:
123 becomes 321-123 becomes -321120 becomes 21The catch is that the answer must still fit inside the signed 32-bit range:
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HARDArray, Binary Search, Divide and ConquerTwo arrays are already sorted. If they were merged into one larger sorted array, the task would be to return the middle value.
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HARDArray, Two Pointers, Dynamic Programming, StackThe input is an elevation map where each number is the height of a vertical bar with width 1.
After rain falls, water can sit in the valleys between taller bars. The task is to compute the total amount of water that stays trapped.
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MEDIUMArray, Two Pointers, GreedyThe input is an array of heights. Each height represents a vertical line drawn at that index.
The task is to pick two lines that, together with the x-axis, form a container that holds the most water.
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MEDIUMLinked List, Math, RecursionTwo linked lists represent two non-negative integers. Each node stores one digit, and the digits are already in reverse order, so the ones place comes first.
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