Master algorithms.

Find two numbers that add up to a target.

Maximize profit from a single buy-sell transaction.

Find contiguous subarray with largest sum.

Check if brackets are correctly matched.

Ways to climb n stairs taking 1 or 2 steps.

Search a target in a sorted array.

Reverse a sequence (array representing linked list).

Count groups of anagrams in a word list.

Count islands in a 0/1 grid (rows as strings).