Sliding Window
Solve fixed-window problems: maximum sum of k elements, moving averages, and O(n) updates as the window slides.
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Prefix Sum
Precompute running totals so the sum of any range can be answered instantly instead of adding it up every time.
Prefix Sum Practice Problems
Easy
2 problemsMedium
6 problems- 111medium
Subarray Sum Equals K
Count how many contiguous subarrays add up to a target value.
- 112medium
Product of Array Except Self
Return an array where each element is the product of every other element, without using division.
- 113medium
Contiguous Array
Find the longest contiguous subarray with an equal number of 0s and 1s.
- 114medium
Range Sum Query 2D - Immutable
Answer repeated queries for the sum of values inside a rectangle of a fixed grid.
- 266medium
Continuous Subarray Sum
Check whether a contiguous subarray of size at least two sums to a multiple of k.
- 267medium
Maximum Size Subarray Sum Equals k
Find the longest contiguous subarray that sums to exactly k.
Hard
1 problemsRelated concepts
Two Pointers
Scan a sorted array or string from both ends at once to find pairs, remove duplicates, or reverse data in O(n).
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Binary Search
Cut a sorted range in half on every step to find a value or boundary in O(log n) instead of checking one by one.
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Depth-First Search
Explore as far as possible down one path before backtracking, used to walk trees, graphs, and grids.
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Breadth-First Search
Explore level by level from a starting point, the go-to way to find the shortest path in an unweighted graph.
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Dynamic Programming
Break a problem into overlapping subproblems and reuse their answers to avoid recomputing the same work.
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