hash map - OpenGenus IQ: Computing Expertise & Legacy

4 Sum problem

In this article, we have explored an insightful approach/ algorithm to find the 4 elements in an array whose sum is equal to the required answer (4 Sum problem). This concept finds many uses in computational geometry.

Algorithms

Longest substring without repeating characters

In this article, we have explained three approaches to the problem of finding Longest substring without repeating characters. This involves the use of Hash Map with the clever use of start and end index.

Algorithms

Intersection of two arrays

We have explored several approaches to find Intersection of two arrays efficiently. This involve techniques like sorting, binary search, hash map and much more.

Algorithms

Longest Increasing Consecutive Subsequence

We have to find the Longest Increasing Consecutive Subsequence in N elements. We can solve this problem efficiently using Dynamic Programming in O(N) time.

Algorithms

Number of Substrings with distinct characters

We have explored various algorithms that will help us in determining the number of substrings that a string can have with distinct characters.

Algorithms

Least frequent element in an array

Given an array of N elements, our task is to find the least frequent element present in it. In this article, we are going to talk about 3 methods to solve this problem along with their implementation.

Algorithms

Finding 2 elements with difference k in a sorted array

This article discusses how to check the existence of and find 2 elements with difference k in sorted array. We have explored 3 approaches and solved it in linear time O(N).

Algorithms

3 Sum problem (Triplets with given Sum)

Given an array, we need to find if there is a triplet in the array whose sum is equal to a given value. If such a triplet is present, we need to print it and return true. Else, return false.

Algorithms

2 Sum: Number of pairs with a given sum

We will find out how we can count the number of pairs in an array whose sum is equal to a certain number. Brute force approaches will take O(N^2) time but we can solve this in O(N) time using a Hash Map.

Algorithms

Finding number of pairs with a certain XOR value

In this article, we are going to find the number of pairs in an unsorted array, whose XOR values matches with our target value (say K). Using our efficient approach (with Hash map), we can solve this in O(N) time complexity while the brute force approach takes O(N^2) time complexity

Algorithms

Implement Least Recently Used (LRU) Cache

In this article, we have implemented Least Recently Used cache using 2 data structures: Doubly Linked Lists and Hash Map and compared LRU with FIFO cache.

Data Structures

Hash Map / Hash table

Hash map (hash table, unordered map, dictionary, hash set) is a widely used efficient data structure that used to store data which can be searched in constant time O(1). This data structure is implemented over an array that maps keys to values that is it is a set of key value pairs.

Software Engineering

HashMap in Java

In Java, HashMap is a Map based collection class that is used for storing Key and value pairs which is denoted as HashMap. It does not maintain order of elements, allows one null key, multiple null values, is not thread safe, default size is 16, default load factor is 0.75 JDK1.7, JDK1.8