Hash-Map

Construct a binary tree from preorder and inorder traversal sequences.

Create a deep copy of a linked list where each node has a random pointer

Find the minimum window substring that contains all characters of another string

Find the single number that appears once in an array where every other number appears twice.

Find the smallest substring that contains all characters of a given pattern

Sort characters in string by frequency using heap or bucket sort

Find the minimum number of intervals the CPU will take to finish all given tasks with a cooldown period between identical tasks

Solve LeetCode 347 Top K Frequent Elements (Medium) with frequency map + bucket sort O(n) or min-heap O(n log k). Step-by-step for interviews.

Find two numbers in an array that add up to a target value.

Given an array of integers and a target, return indices of two numbers that add up to the target.

Traverse a binary tree vertically and return nodes by columns