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You are here: Home » collections » HashMap

Java: How to get all keys by a value in HashMap ? | Search by Value in Map

Varun January 21, 2018 Java: How to get all keys by a value in HashMap ? | Search by Value in Map2018-01-21T16:15:15+05:30 collections No Comment
In this article we will discuss how to search into a Map by value and fetch associated keys to the given value. (more…)
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Java : How to update the value of an existing key in HashMap | put() vs replace()

Varun January 13, 2018 Java : How to update the value of an existing key in HashMap | put() vs replace()2018-01-13T17:59:50+05:30 collections No Comment
In this article we will discuss different ways to update the value of an existing key in HashMap in Java. (more…)
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Java : Creating HashMap by associating multiple values with same Key

Ritika June 4, 2017 Java : Creating HashMap by associating multiple values with same Key2017-06-04T18:48:02+05:30 collections No Comment
In this article we will discuss how to create a HashMap with multiple values associated with same Key in Java. (more…)
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Java : How to Remove elements from HashMap while Iterating

Varun June 3, 2017 Java : How to Remove elements from HashMap while Iterating2017-06-03T17:24:52+05:30 collections No Comment
In this article we will discuss different ways to remove elements from HashMap while Iterating. (more…)
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HashMap Tutorials

  • What is Hashing and Hash Table?
  • Associating Multiple values with same Key
  • Remove elements while Iterating
  • Update the value of an existing key
  • Get all keys by a value in HashMap

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Python : List

  • Check if an item exists in List
  • Check if a list contains all the elements of other list
  • Create a List and initialize with values
  • How to Iterate over a List
  • Insert an element at specific index in List
  • Sort a list of tuples by 2nd Item
  • Sort a list of strings
  • Add an element in list | append() vs extend()
  • Check if all elements in a List are same
  • Merge / Join two or more lists
  • How to find all indexes of an item in a List ?
  • Count elements in a list, lists of lists or nested list
  • Remove Duplicates from a List
  • Convert a list to string
  • Remove element from a list by value or Index
  • Remove multiple elements from list
  • Count elements in a list that satisfy certain conditions

Python : Dictionary

  • Creating Dictionaries in Python
  • Iterating over Dictionaries in Python
  • Check if a key exists in Dictionary
  • Get list of all the keys in Dictionary
  • Get list of all the Values in a Dictionary
  • Remove multiple keys in Dictionary while Iterating
  • Remove a key from Dictionary
  • Add key/value pairs in Dictionary
  • Find keys by value in Dictionary
  • Sort a Dictionary by key or Value
  • Copy a dictionary | Shallow vs Deep Copy
  • Convert a list to dictionary
  • Filter a dictionary by conditions on keys or values
  • Python : How to get all keys with maximum value in a Dictionary
  • How to Merge two or more Dictionaries in Python ?

Python Strings

  • Access characters in string by index in Python
  • Iterate over the characters in string
  • How to Replace characters in a string ?
  • How to remove characters from a string by Index ?
  • How to pad strings with zero, space or some other character in Python
  • How to Compare Strings ? | Ignore case | regex | is vs == operator using Python
  • Find occurrence count & all indices of a sub-string in another string | including overlapping sub-strings
  • Check if a String contains a sub string & find it’s index | case insensitive
  • Find frequency of each character in string and their indices | Finding duplicate characters in a string
  • How to create multi line string objects in python ?
  • Count occurrences of a single or multiple characters in string and find their index positions

Python : Functions

  • *args | Pass multiple arguments to function
  • **kwargs | Pass variable length key value pair as arguments to Function
  • Unpack list, tuple or dictionary to Function arguments
  • Why do we need Lambda functions in Python ? | Explained with examples.
  • How to use if, else if & else in Lambda Functions
  • How to use global variables in a function ?
  • Python : map() function explained with examples
  • Delete elements from a Numpy Array by value or conditions in Python
  • Python : filter() function | Tutorial & Examples
  • Python : max() function explained with examples
  • Python : min() function Tutorial with examples

Java – Hashmap

  • What is Hashing and Hash Table?
  • Associating Multiple values with same Key
  • Remove elements while Iterating
  • Update the value of an existing key
  • Get all keys by a value in HashMap

Java – HashSet

  • What is Hashing and Hash Table?
  • Create and add elements in a HashSet
  • Iterate over a HashSet
  • Search for an element in HashSet
  • Merge two HashSets
  • Initializing HashSet from an Array
  • Convert a HashSet into an Array
  • Merge an Array in a HashSet

Java Interview Questions

  • Method Overriding Tutorial
  • Overriding with Different Return Type
  • Calling Base class’s overridden method
  • Preventing Method Overriding
  • Need of preventing Method Overriding

Pandas

  • Create DataFrame from dictionary in pandas
  • Get list of column and row names in DataFrame
  • Change Column & Row names in DataFrame
  • Select Rows & Columns using loc & iloc in DataFrame
  • Select Rows based on conditions
  • Drop rows in DataFrame by index labels
  • Drop rows in DataFrame by conditions on column values
  • Drop columns in DataFrame by label Names or Position
  • Add new columns in a dataFrame
  • How to add rows in a DataFrame
  • Count NaN or missing values in DataFrame
  • Convert lists to a dataframe
  • Find & Drop duplicate columns in a DataFrame
  • Create an empty DataFrame and add data to it later
  • Pandas : Check if a DataFrame is empty in Python
  • Pandas : Find duplicate rows in a Dataframe based on all or selected columns using DataFrame.duplicated() in Python
  • Pandas : skip rows while reading csv file to a Dataframe using read_csv() in Python
  • pandas.apply(): Apply a function to each row/column in Dataframe
  • Pandas: Sort rows or columns in Dataframe based on values using Dataframe.sort_values()
  • Pandas: Find maximum values & position in columns or rows of a Dataframe
  • Pandas : How to Merge Dataframes using Dataframe.merge() in Python – Part 1
  • Pandas : Merge Dataframes on specific columns or on index in Python – Part 2
  • Pandas : How to merge Dataframes by index using Dataframe.merge() – Part 3
  • Pandas : count rows in a dataframe | all or those only that satisfy a condition
  • Pandas : Read csv file to Dataframe with custom delimiter in Python
  • Pandas : 6 Different ways to iterate over rows in a Dataframe & Update while iterating row by row
  • Pandas : Loop or Iterate over all or certain columns of a dataframe
  • Get minimum values in rows or columns & their index position in Dataframe using Python
  • Apply a function to single or selected columns or rows in Dataframe
  • Sort a DataFrame based on column names or row index labels using Dataframe.sort_index() in Pandas
  • Pandas : Drop rows from a dataframe with missing values or NaN in columns
  • Get unique values in columns of a Dataframe in Python
  • Change data type of single or multiple columns of Dataframe in Python
  • Check if a value exists in a DataFrame using in & not in operator | isin()
  • Select first or last N rows in a Dataframe using head() & tail()

Numpy

  • Create a numpy array from list, tuple or list of lists
  • Find the index of value in Numpy Array
  • Select element or sub array by index from numpy array
  • Select rows / columns by index from a 2D numpy array
  • Select elements by conditions from Numpy Array
  • Create a Numpy Array of evenly spaced numbers
  • How to append elements to a Numpy Array
  • Find max value & it’s index in Numpy Array | numpy.amax()
  • Find unique values in a numpy array with frequency & indices
  • numpy.where() : Tutorial & Examples | Python
  • numpy.zeros() & numpy.ones() | Create a numpy array of zeros or ones
  • Create Numpy Array of different shapes & initialize with identical values using numpy.full()
  • numpy.amin() | Find minimum value in Numpy Array and it’s index
  • numpy.linspace() | Create same sized samples over an interval in Python
  • Delete elements, rows or columns from a Numpy Array by index positions using numpy.delete() in Python
  • How to get Numpy Array Dimensions using numpy.ndarray.shape & numpy.ndarray.size() in Python
  • Sorting 2D Numpy Array by column or row in Python
  • How to Reverse a 1D & 2D numpy array using np.flip() and [] operator in Python
  • How to save Numpy Array to a CSV File using numpy.savetxt() in Python
  • What is a Structured Numpy Array and how to create and sort it in Python?
  • How to sort a Numpy Array in Python ?

Python: Date Time Tutorials

  • Convert a timestamp string to a datetime object
  • Get Current date and timestamp
  • Get Last Modification date & time of a file

C++11 – Utilities

  • Deleting Functions using ‘delete’ keyword
  • std::bind
  • auto specifier
  • Variadic Templates

C++11 Smart Pointers

  • shared_ptr<> Tutorial and Examples
  • shared_ptr and Custom Deletor
  • shared_ptr vs raw pointer
  • Create shared_ptr objects carefully
  • weak_ptr Tutorial | shared_ptr and Cyclic References
  • unique_ptr<> Tutorial and Examples

C++11 – Unordered Set

  • 1.) unordered_set Basic Example
  • 2.) Initializing an unordered_set
  • 3.) Inserting elements in an unordered_set
  • 4.) Searching an element in unordered_set
  • 5.) unordered_set – Custom Hasher & Comparator
  • 6.) Unordered_set & User defined classes

C++11 – UnorderedMap

  • Basic Usage Detail and Example
  • Initializing an unordered_map
  • Searching in unordered_map
  • Insert elements in unordered_map
  • Erasing an element
  • Erase elements while iterating
  • std::map vs std::unordered_map

C++11 Multithreading

  • Part 1: Three Ways to Create Threads
  • Part 2: Joining and Detaching Threads
  • Part 3: Passing Arguments to Threads
  • Part 4 : Sharing Data & Race Conditions
  • Part 5 : Fixing Race Conditions using mutex
  • Part 6 : Need of Event Handling
  • Part 7: Condition Variables
  • Part 8: std::future and std::promise
  • Part 9: std::async Tutorial & Example
  • Part 10: std::packaged_task<> Tutorial

C++11 Rvalue References

  • lvalue vs rvalue
  • Is rvalue immutable in C++?
  • What is rvalue reference in C++11
  • Move Contsructor

Callbacks in C++

  • Function Pointers
  • Function Objects & Functors

Design Patterns

  • Behavioral Design Patterns
    • Observer Design Pattern
    • State Design Pattern
    • Strategy Design Pattern
  • Structural Design Patterns
    • Composite Design Pattern
    • Flyweight Design Pattern
  • Creational Design Patterns

Pointers

  • Pointer vs Refrence
  • Allocating 2D Array Dynamically

C++ Strings

  • Find and Replace all occurrences of a string
  • Find all occurrences of a sub string
  • Case Insensitive string::find
  • Convert First Letter of each word to Upper Case
  • Converting a String to Upper & Lower Case
  • Trim strings in C++
  • C++ : How to split a string using String and character as Delimiter?
  • startsWith() Implementation
  • endsWith() Implementation
  • Remove Sub Strings from String

Polymorphism

  • Virtual Functions
  • vTable and vPointer

STL – Vector

  • 1.) What’s std::vector and why to use it?
  • 2.) Different ways to initialize a vector
  • 3.) How does std::vector works internally
  • 4.) User Defined Objects & std::vector
  • 5.) How to use vector efficiently in C++?
  • 6.) std::vector and Iterator Invalidation
  • 7.) Remove repeated elements from a vector
  • 8.) Fill a vector with random numbers
  • 9.) Hidden cost of std::vector
  • 10.) Adding elements in Vector

STL – Deque

  • 1.) What is std::deque and how deque works internally.
  • 2.) deque vs vector : What to choose ?

STL – List

  • 1.) std::list Internals & Usage Details
  • 2.) List vs Vector
  • 3.) Different ways to Initialize a list
  • 4.) Erase elements using iterators
  • 5.) Remove elements while Iterating
  • 6.) Remove elements based on External Criterion
  • 7.) Get element by index in List
  • 8.) Searching an element in std::list
  • 9.) Different Ways to iterate over a List
  • 10.) Sorting a List & custom Comparator

STL – Set

  • 1.) C++ Set basic example and Tutorial
  • 2.) Using std::set with user defined classes
  • 3.) std::set and external Sorting criteria | Comparator
  • 4.) Access Element by index in Set
  • 5.) How to insert elements in Set
  • 6.) How to iterate over a Set
  • 7.) Removing an element from Set
  • 8.) Erase elements while Iterating & Generic erase_if()

STL – Map

  • 1.) std::map Usage Detail with examples
  • 2.) std::map and Comparator
  • 3.) std::map & User defined class objects as keys
  • 4.) Set vs Map
  • 5.) How to Iterate over a map in C++
  • 6.) Map Insert Example
  • 7.) Iterate a map in reverse order
  • 8.) Check if a key exists in a Map
  • 9.) Search by value in a Map
  • 10.) Erase by Key | Iterators
  • 11.) C++ Map : Operator []
  • 12.) Erase by Value or callback
  • 13.) copy all Values from a Map to vector

STL Multimap

  • MultiMap Example and Tutorial
  • multimap::equals_range – Tutorial

STL Algorithms

  • std::sort Tutorial & Example
  • std::unique Tutorial & Example
  • 1.) Using std::find & std::find_if with User Defined Classes
  • 2.) Iterating over a range of User Defined objects and calling member function using std::for_each

C++ Memory Manangement

  • Memory Leaks
  • new and delete operator
  • delete vs []delete
  • Out Of Memory Errors
  • Overload new & delete
  • Restrict Dynamic Deletion
  • Placement new operator
  • Delete ‘this’ pointer

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