dsa2 min read
Shuffle an Array — Fisher-Yates O(n) Uniform Shuffle [Google Easy]
Implement Fisher-Yates shuffle for uniform random permutation. Every arrangement is equally probable. O(n) time O(1) extra space.
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dsa2 min read
Running Sum of 1D Array — Prefix Sum Foundation [Amazon Easy]
Compute running (prefix) sum in O(n) time O(1) extra space. The prefix sum pattern is foundational for range queries, subarray problems and 2D matrices.
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dsa3 min read
3Sum — Sort + Two Pointers O(n²) Deduplication [Google, Meta, Amazon]
Find all unique triplets summing to zero. Sort array then fix one element and use two pointers. Full O(n²) solution in C, C++, Java, JavaScript and Python.
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dsa2 min read
Container With Most Water — Greedy Two Pointer O(n) [Google, Meta]
Find two lines that together with the x-axis form a container holding the most water. Greedy two-pointer O(n) — never check a pair that can't be optimal.
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dsa2 min read
Product of Array Except Self — Prefix × Suffix O(n) O(1) [Google, Meta, Amazon]
Compute product of all elements except self without division. O(n) two-pass prefix/suffix approach with O(1) extra space.
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