Given a string, determine the length of the longest substring that contains no repeating characters. The substring must consist of consecutive characters, and its length is to be returned as the output.
Given a string, find and return the longest palindromic substring in it. A palindrome is a word that reads the same forward and backward. The substring must be contiguous within the original string.
Given a string, write it in a zigzag pattern on a specified number of rows and then read the rows line by line to create the final string. Return this transformed string.
You are given a positive integer and need to convert it into a Roman numeral. Roman numerals are constructed by combining symbols from the set: I, V, X, L, C, D, M, where each symbol has a specific value. The conversion rules are based on subtractive notation for values like 4 (IV), 9 (IX), and so on, to avoid using symbols multiple times where not allowed.
