dsa2 min read
Reverse Pairs [Hard] — Merge Sort with Cross-Half Counting
Count pairs (i,j) where i<j and nums[i]>2*nums[j] using modified merge sort to count cross-half pairs before merging.
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dsa1 min read
Split Array Largest Sum [Hard] — Binary Search on Answer
Minimize the largest sum among m subarrays by binary searching on the answer and greedy checking feasibility.
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Shortest Subarray with Sum ≥ K [Hard] — Deque on Prefix Sums
Find the shortest subarray with sum >= K using a monotonic deque on prefix sums, handling negative numbers correctly.
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Count of Range Sum [Hard] — Merge Sort on Prefix Sums
Count the number of range sums that lie in [lower, upper] using a merge sort approach on prefix sums.
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Maximum Sum of 3 Non-Overlapping Subarrays [Hard] — Sliding Window + DP
Find three non-overlapping subarrays of length k with maximum sum using sliding window sums and left/right best index arrays.
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