Knowledge Factory

When preparing for coding interviews, especially with top companies like MAANG (Meta, Apple, Amazon, Netflix, Google), it's essential to have a strong grasp of common data structures and algorithms, including HashMap. Below are some common HashMap-related coding problems you might encounter, along with a brief explanation and Java solutions. 1. Two Sum (Using HashMap) Problem: Given an array of integers and a target sum, find two numbers such that they add up to the target. Solution using HashMap: import java.util. HashMap ; public class TwoSum { public int [] twoSum( int [] nums, int target) { HashMap <Integer, Integer> map = new HashMap <>(); for ( int i = 0 ; i < nums.length; i++) { int complement = target - nums[i]; if ( map .containsKey(complement)) { return new int [] { map . get (complement), i }; } map .put(nums[i], i); } throw new IllegalArgume...

Below is a list of MAANG DSA Interview Questions with insights and their implementation in Java to help you understand their significance and approach: 1. Two Sum Problem: Given an array of integers nums and an integer target , return the indices of the two numbers such that they add up to target . Insight: Brute Force: Check every pair. O(n²) time complexity. Optimized: Use a HashMap to store the difference between the target and the current value. O(n) time complexity. Java Implementation: import java.util. HashMap ; public class TwoSum { public static int [] twoSum( int [] nums, int target) { HashMap <Integer, Integer> map = new HashMap <>(); for ( int i = 0 ; i < nums.length; i++) { int complement = target - nums[i]; if ( map .containsKey(complement)) { return new int []{ map . get (complement), i}; } map .put(nums[i], i); } throw new IllegalArgum...