Arrays & Hashing

Find two numbers in a sorted array that add up to target

Find two lines that form container holding most water

Find all unique triplets that sum to zero

Calculate how much rain water can be trapped between bars

Rotate array to the right by k steps using triple reverse

Find all unique quadruplets that sum to target

Find intersection of two arrays including duplicates

Remove duplicates allowing at most two of each element

Find two numbers that add up to target using hash map

Check if array contains any duplicate values using Set

Check if two strings are anagrams using character frequency

Return the index of the first non-repeating character

Check if ransomNote can be built from magazine letters

Group strings that are anagrams of each other

Find the k most frequent elements using bucket sort

Calculate product of all elements except self without division

Find length of longest consecutive sequence in O(n)

Find maximum profit from one buy and one sell

Find contiguous subarray with largest sum using Kadane algorithm

Find element appearing more than n/2 times using Boyer-Moore

For each day, find how many days until a warmer temperature

Find next greater element for each value in nums1 based on nums2

Find next greater element in a circular array

Find the largest rectangle area in a histogram

Count connected components of land cells in a 2D grid

Fill connected pixels in an image with a replacement color

Find the largest connected land area in a binary grid

Merge all overlapping intervals — classic FAANG sorting problem

Can a person attend all meetings? Check for overlapping intervals

Find minimum number of conference rooms needed

Sort characters by how often they appear, most frequent first

Sort array according to the order defined by another array

Move all even numbers before odd numbers

Find the kth largest element using QuickSelect (partition)

Insert a new interval and merge if necessary