Java programs that complete the following:

using hashmaps and not loops, returns the most common character when given a string

Reverses a hashmap. It can contain multiple keys with the same value and this causes the values of the reversed map to be a list.

An array of temperatures and an array of the cities where each temperature is from is given. The name of a city that experienced a temperature drop is then returned. If there is no city that experienced a drop,return null.

Given a 2D array populated with a sequence of characters that wrap from the rightmost position to the leftmost position on the next row, find the length of the longest sequence of repeated characters.