Longest Consecutive Sequence: Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.

Find the Duplicate Number: Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive.

Find All Numbers Disappeared in an Array: Given an array nums of n integers where nums[i] is in the range [1,n], return an array of all the integers in the range [1,n] that do not appear in nums.

Find All Duplicates In Array: Given an integer array nums of length n where all the integers of nums are in the range [1, n] and each integer appears once or twice, *return an array of all the integers that appears twice*.

Convert 1D Array into 2D Array: You are given a 0-indexed 1-dimensional (1D) integer array original, and two integers, m and n.

Contains Duplicate: Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.