Hashing in Data Structure

Hashing is a technique used in data structures that efficiently stores and retrieves data in a way that allows for quick access.

• Hashing involves mapping data to a specific index in a hash table (an array of items) using a hash function. It enables fast retrieval of information based on its key.
• The great thing about hashing is, we can achieve all three operations (search, insert and delete) in O(1) time on average.
• Hashing is mainly used to implement a set of distinct items (only keys) and dictionaries (key value pairs).

Here’s an example of hashing using the modulo method. The hash function H(x) = x % 10 converts any large number into a smaller value between 0 and 9.

Basics

• Introduction
• Applications
• Separate Chaining for Collision Handling
• Open Addressing for Collision Handling

Easy Problems

• Check tor Subset
• Check for Disjoint
• Check for Equal
• Fizz Buzz
• Max distance between two occurrences
• Duplicate within K Distance
• Intersection of Two Arrays
• Union of Two Arrays
• Most Frequent Element
• 2 Sum - Find if there is any pair
• 2 Sum - Count Pairs
• Count Pairs with Given Diff
• Only repetitive element from 1 to n-1
• Missing of a Range
• Missing from Min to Max of Array
• Minimum Subsets with distinct
• Minimum Removals for No Common
• Maximum points on the same line

Medium Problems

• Pair Sums Divisible by k
• Subarray with sum divisible by k
• 3 Sum - Count all triplets with Given sum
• 3 Sum – Find All Triplets with Zero Sum
• Itinerary from a given list of tickets
• Longest Subarray with Majority Greater Than K
• Number of Employees Under every Employee
• Largest subarray with 0 sum
• Subarray with given sum
• Longest Consecutive subsequence
• Largest Fibonacci Subset
• Consecutive Subset Partitioning
• Distincts in every window of size k
• Insert, delete, search and getRandom
• Min insertions for a palindrome permutation
• Smallest subarray with k distinct numbers
• All pairs (a, b) in an array such that a % b = k
• Group words with same set of characters
• k-th distinct (or non-repeating) .

Hard Problems

• Represent Fraction as String
• 4 Sum – Count quadruplets
• 4 Sum – Find all Quadruplets
• 4 Sum - From four sorted arrays
• Largest subarray with equal 0s and 1s
• Longest Common Sum Span
• Palindrome Substring Queries
• Subarrays having distinct count
• Maximum array from two arrays
• Sum of all unique sub-array sums.
• Recaman’s sequence
• Longest strict bitonic subsequence
• Duplicate Subtrees
• Submatrix with corners as 1

Quick Links :

• Practice Problems on Hashing
• Hashing Interview Questions
• Quiz on Hashing
• DSA Tutorial