dsa2 min read
Maximum Product Subarray — Track Min and Max O(n) [Google, Meta, Amazon]
Find the maximum product of a contiguous subarray. Track both min and max at each position (negative * negative = positive). O(n) time O(1) space.
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dsa1 min read
Rotate Image 90 Degrees — Transpose + Flip O(n²) [Meta, Google]
Rotate an n×n matrix 90 degrees clockwise in-place. Trick: transpose (swap i,j with j,i) then reverse each row. O(n²) time O(1) space.
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dsa3 min read
Next Permutation [Medium] — In-Place Rearrangement
Find the lexicographically next permutation in-place using a two-pass scan from the right.
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dsa2 min read
Find the Duplicate Number [Medium] — Floyd's Cycle Detection
Find the one duplicate in [1..n] without modifying the array using Floyd's tortoise-and-hare cycle detection.
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dsa2 min read
Sort Colors [Medium] — Dutch National Flag Algorithm
Sort an array of 0s, 1s, and 2s in-place in one pass using Dijkstra's Dutch National Flag algorithm.
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