Minimum window Substring AND longest Substring with at most K distinct characters

Given a gif, each cell can have one of the three values. 0 for empty, 1 for fresh Orange and 2 for rotten. Return minimum number of minutes that must elapse until no cell has a fresh Orange

Given a grid, find number of islands. We use depth first search.

Traverse a tree or a graph using DFS and BFS

Given a an array of Sorted K linked lists, merge all K lists in one Sorted linked-list and return it.

Find two numbers that add up to a Target. Find two numbers in a sorted array that add up to a number. Find three numbers in an array that add up to a Target.

Given a Unix style absolute path, simplify it and return the shortest canonical path

Design In-Memory file system to simulate following functions. LS, mkdir, addcontentstofile, rewdcontentsfromfile

Give a string S and a String T, find the minimum window in S which will contain all characters in T.

Given a list of scheduled for employees in a company, return free time where no employee is working.

Find a celebrity in a room where everyone knows the celebrity and celebrity doesn’t know anyone.