Tag Archives: HashMap

Internal working of HashMap in Java 8 & Beyond

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How HashMap internally works in java is the most asked interview question. Even with just 1–2 years of experience, you’ve likely used HashMap in your code. However, many developers are unaware of how it actually works under the hood.

This article dives deep into the internal mechanics of HashMap, explaining how the get, put, operations work behind the scenes. I am going to discuss the internal working of HashMap in java with diagrams and code examples.

How HashMap works internally video tutorial

What Really Happens When You Instantiate a HashMap in Java

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Find Majority Element in an Array

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Given an array of size n, Write a code to find majority element in an array.

What is Majority Element?

The majority element is the element that appears more than n/2 times where n is the size of an array.

NOTE: For this problem you can assume that the array is non-empty and the majority element always exist in the array.

Example 1:

Input : [3, 2, 3]

Output: 3

The size of the array is 3 and the element which occurs more than 1 is the majority element. So three is the output.

Example 2:

Input: [2, 2, 1, 1, 1, 2, 2]

Output: 2

The element 2 occurs more than 3 times. So, It is the majority element.

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Insert Delete GetRandom o(1) Solution

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In this problem, We have to design a data structure that supports Insert, Delete, and GetRandom in average O(1) time.

OR

Design a data structure that supports insert, delete, and getRandom in constant time O(1).

insert(value): Inserts an item value to the set if it’s not present.

remove(value): Removes an item value from the set if present.

getRandom(): Returns a random element from current set of elements. Each element must have the same probability of being returned.

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