Find the unique element in an array where all elements appear twice except one.Examples: Summary (with approach)Use XOR: since a ^ a = 0, a ^ 0 = a, and XOR is associative/commutative, XOR all numbers; the result is the single number. Runs in O(N) time and O(1) space. Alternative: hash counting in O(N) space….

Imagine an array that contains both integers and nested arrays, such as the following:[8, 4, [5, [9], 3], 6].The depth sum is described as the weighted sum of each integer, weighted by their respective depths. In the example, 8’s depth is 1, while 9’s is 3.Given such an array, calculate its depth sum. Examples Summary…

You are given K sorted integer arrays (non-decreasing). Arrays may contain duplicates within the same array and across different arrays.Return a sorted list of unique integers that appear in any of the arrays (i.e., the set union, sorted). Example:A = [-100, -1, -1, 0, 5]B = [0]C = [-1, 0, 0]Output → [-100, -1, 0,…

Given the root of a binary search tree, return a balanced binary search tree that contains the same node values. If there is more than one valid answer, return any of them.A binary search tree is balanced if the depth of the two subtrees of every node never differs by more than 1. Example:Input: root…

Problem (English original):Given the root of a binary tree containing integers, return a list of all the integers in the tree ordered by column from left to right. Within each column, values should be ordered from top to bottom. Assume a node definition (or language equivalent): Input (example, ASCII tree): Output (example): Summary (approach):BFS/DFS tagging…

Given a string S consisting of lowercase English characters, determine if you can make it a palindrome by removing at most one character. Example: Summary (approach):Use two pointers. On the first mismatch, try skipping either the left or the right character and check if the remaining substring is a palindrome. O(n) time, O(1) space. The VOprep team…

Problem (verbatim):“A multiset (also known as a bag) is a mutable, unordered collection of distinct objects that may appear more than once in the collection. Implement a multiset that implements the following methods:• add(element)• remove(element)• count(for: element)” English summary (concise approach):Back the multiset with a hash map value → frequency. The VOprep team has long accompanied candidates…

Problem (verbatim):“Given an integer array and an integer number k. Return the k-th largest element in the array. Examples:• array = [5, −3, 9, −1]• k = 0 ⇒ return: 9• k = 1 ⇒ return: 5• k = 3 ⇒ return: −3” summary (concise approach):Return the k-th largest (0-indexed) value. The VOprep team has long accompanied…

Problem Statement (English original)Assume a binary-tree node: Given the root of a binary tree, output the node values in vertical order (column order) from leftmost column to rightmost column.Within each column, list nodes top-to-bottom in the order they are encountered by a standard BFS (or by row index if you compute coordinates). Illustrative example (matching…

Problem Statement (English original)You are given a current working directory cwd (an absolute Unix-style path) and a cd(arg) string which can be either an absolute path (starts with /) or a relative path (may include segments . and ..).Implement a function that returns the normalized absolute path after applying cd(arg) from cwd. Rules: Examples (from…