#Arrays

Given an array, find all unique quadruplets (a, b, c, d) such that a * b = c * d. Please ensure to handle duplicates and return the unique sets.

Given an array of integers where every element appears twice except one, return the element that appears once.

You are given an integer array of length n. Return a new array of the same length where each element represents the sum of the value at the index with its neighboring elements.

Given an array of integers, find indices of the two numbers such that they add up to a specific target. Implement an optimal solution using a HashMap with a time complexity of O(n).

Answer a DSA question focused on arrays and sorting algorithms.