Return every pair of distinct elements that add up to a target — a classic interview problem with an efficient hash-based O(n) solution.

Compute cumulative sums (running totals) — each element in the result is the sum of all preceding elements plus itself. Useful for financial calculations, progress tracking, and time series data.

Count element occurrences and return the one that appears most often — useful for analytics, voting systems, and mode calculations.

Use Array#flatten with a depth argument to collapse nested arrays to a precise level — avoiding full flattening when partial structure needs to be preserved.

Perform a recursive hash merge that combines nested values instead of overwriting them — useful for configuration merging, settings overrides, and building complex data structures.

Use sort_by to order a hash’s key-value pairs by value, returning a sorted array of pairs that can be converted back to a hash.

Use chunk_while to group adjacent array elements that share a condition — perfect for run-length encoding, streak detection, and range grouping.

Produce every possible ordering of array elements using Array#permutation.

Determine whether two strings contain the same characters in any order.

Shift array elements left or right by N positions using Array#rotate.

Deduplicate an array in insertion order using Array#uniq.

Combine elements from two or more arrays by position using Array#zip.

Detect which values appear more than once in an array using group_by or tally.

Generating cryptographically secure random tokens is essential for password reset links, API keys, email verification tokens, and any value that must be unpredictable to an attacker.

When displaying large datasets in pages — or processing records in batches — you need to split an array into fixed-size chunks. Ruby’s each_slice handles this cleanly without manual index arithmetic.